Re: [sqlalchemy] avoid setting attribute on init and or.reconstructor

[lars van gemerden]

Thanks Mike, I oversimplified a little bit (the factory function takes more 
arguments than self.stops, not part of the Planning class), but if i create 
the factory with partial I think it will work. 

On Monday, November 16, 2020 at 6:16:24 PM UTC+1 Mike Bayer wrote:

> I would use a memoized descriptor for that and have it evaluate when 
> called.
>
> Amazingly, i can't find public examples of Python memoize decorators that 
> aren't overwrought.we use one that is completely efficient and simple:
>
> class memoized_property(object):
> """A read-only @property that is only evaluated once."""
>
> def __init__(self, fget, doc=None):
> self.fget = fget
> self.__doc__ = doc or fget.__doc__
> self.__name__ = fget.__name__
>
> def __get__(self, obj, cls):
> if obj is None:
> return self
> obj.__dict__[self.__name__] = result = self.fget(obj)
> return result
>
>
> then you can just set it up as:
>
> class Planning(...):
> @memoized_property
>     def matrix(self):
> return self.matrix_factor(self.stops)
>
>
>
>
> On Mon, Nov 16, 2020, at 11:43 AM, lars van gemerden wrote:
>
> Hi Mike,
>
> What if during reconstruction you need a one-to-many attribute, like:
>
> class Planning(SqlaBase):
> stops = relationship(*"Stop"*, back_populates=*"planning"*, lazy=
> *"joined"*)
>
> matrix_factory = Matrix
>
> def __init__(self, **kwargs):
> super().__init__(**kwargs)
> self.matrix = self.matrix_factory(self.stops)
>
> @reconstructor
> def init_on_load(self):
>  self.matrix = self.matrix_factory(self.stops)
> The docs say self.stops will not be completely loaded in init_on_load, how 
> could i make this work?
>
> Cheers, Lars
> On Monday, August 7, 2017 at 6:09:08 AM UTC+2 Mike Bayer wrote:
>
>
>
> On Aug 6, 2017 1:33 PM, "Shane Carey"  wrote:
>
> Hey Mike,
>
> I can expand my example. I have an orm mapped attribute like this
>
> class Obj(Base):
> _evaluator = Column(String)
>
> def __init__(self, **kwargs):
> super().__init__(**kwargs)
> self._eval_func = eval(self._evaluator)
>
> @orm.reconstructor
> def init_on_load(self):
> self._eval_func = eval(self._evaluator)
>
> @property
> def evaluator(self):
>  return self._eval_func
>
> @evaluator.setter
> def set_evaluator(ev):
> self._evaluator = ev
> self._eval_func = eval(self._evaluator)
>
> You can see that I have to explicitly set self._eval_func in three 
> different places, when really I just want to set it every time 
> self._evaluator is set.
>
> It looks to me like the orm events are just a different way of placing the 
> different settings of this class attribute
>
> Also, I would like to not call eval in the getter of the property for the 
> sake of performance (I know that would simplify the issue).
>
> Is there a way to intercept the setting of self._evaluator for all cases?
>
>
>
> Use the init and load event listeners from my previous email on top of one 
> function.  It will be called for init and load. 
>
>
>
> -- 
> SQLAlchemy - 
> The Python SQL Toolkit and Object Relational Mapper
>  
> http://www.sqlalchemy.org/
>  
> To post example code, please provide an MCVE: Minimal, Complete, and 
> Verifiable Example. See http://stackoverflow.com/help/mcve for a full 
> description.
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>
>
> -- 
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> The Python SQL Toolkit and Object Relational Mapper
>  
> http://www.sqlalchemy.org/
>  
> To post example code, please provide an MCVE: Minimal, Complete, and 
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Re: [sqlalchemy] avoid setting attribute on init and or.reconstructor

[lars van gemerden]

Hi Mike,

What if during reconstruction you need a one-to-many attribute, like:

class Planning(SqlaBase):
stops = relationship("Stop", back_populates="planning", lazy="joined")

matrix_factory = Matrix

def __init__(self, **kwargs):
super().__init__(**kwargs)
self.matrix = self.matrix_factory(self.stops)

@reconstructor
def init_on_load(self):
 self.matrix = self.matrix_factory(self.stops)

The docs say self.stops will not be completely loaded in init_on_load, how 
could i make this work?

Cheers, Lars
On Monday, August 7, 2017 at 6:09:08 AM UTC+2 Mike Bayer wrote:

>
>
> On Aug 6, 2017 1:33 PM, "Shane Carey"  wrote:
>
> Hey Mike,
>
> I can expand my example. I have an orm mapped attribute like this
>
> class Obj(Base):
> _evaluator = Column(String)
>
> def __init__(self, **kwargs):
> super().__init__(**kwargs)
> self._eval_func = eval(self._evaluator)
>
> @orm.reconstructor
> def init_on_load(self):
> self._eval_func = eval(self._evaluator)
>
> @property
> def evaluator(self):
>  return self._eval_func
>
> @evaluator.setter
> def set_evaluator(ev):
> self._evaluator = ev
> self._eval_func = eval(self._evaluator)
>
> You can see that I have to explicitly set self._eval_func in three 
> different places, when really I just want to set it every time 
> self._evaluator is set.
>
> It looks to me like the orm events are just a different way of placing the 
> different settings of this class attribute
>
> Also, I would like to not call eval in the getter of the property for the 
> sake of performance (I know that would simplify the issue).
>
> Is there a way to intercept the setting of self._evaluator for all cases?
>
>
>
> Use the init and load event listeners from my previous email on top of one 
> function.  It will be called for init and load. 
>
>
> -- 
> SQLAlchemy - 
> The Python SQL Toolkit and Object Relational Mapper
>  
> http://www.sqlalchemy.org/
>  
> To post example code, please provide an MCVE: Minimal, Complete, and 
> Verifiable Example. See http://stackoverflow.com/help/mcve for a full 
> description.
> --- 
> You received this message because you are subscribed to the Google Groups 
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> For more options, visit https://groups.google.com/d/optout.
>
>
>

-- 
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The Python SQL Toolkit and Object Relational Mapper

http://www.sqlalchemy.org/

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[sqlalchemy] a relationship question

[lars van gemerden]

Hi all,

Simple question, but couldn't find it in the docs:

- How can i retrieve the target class in a relationship in the ORM? Say i 
have a sqla class with a relationship("User", primaryjoin = ...), how can i 
retrieve the User class from the relationship ('relationship' is a 
descriptor, right?)


Cheers, Lars  

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Re: [sqlalchemy] join & aliased

[lars van gemerden]

OK, thank you

On Saturday, March 22, 2014 9:03:01 PM UTC+1, Michael Bayer wrote:
>
>
> On Mar 22, 2014, at 9:16 AM, lars van gemerden 
> > 
> wrote: 
>
> > query = session.query(Email) 
> > query = query.join("user") #or query = query.join("user", 
> aliased = True) 
> > query = query.add_columns(Email.email, User.name) 
>
> the add_columns() method does not have the clause adaptation behavior of 
> filter(), so it does not take into account the fact that “aliased=True” was 
> called when the User entity was first pulled in.  so this pulls in the User 
> entity twice, once from User.name, and another because of the aliased(User) 
> brought in by the join. 
>
> solution is not to use aliased=True (a feature I would never have added if 
> it were today), use  ua = aliased(User); q.join(ua, “user”); 
> query.add_columns(ua.name). 
>
>
>
>

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[sqlalchemy] join & aliased

[lars van gemerden]

Hi all,

Maybe (hopefully;-) i am missing something simple, but i have the following 
test code:

engine = create_engine('sqlite:///:memory:', echo=True) 
Session = sessionmaker(bind=engine)   
Base = declarative_base()

class User(Base):
__tablename__ = 'user_table'
id = Column(Integer, primary_key=True)
name = Column(String)

addresses = relationship("Email", back_populates="user")

class Email(Base):
__tablename__ = 'email_table'
id = Column(Integer, primary_key=True)
email = Column(String)
user_id = Column(Integer, ForeignKey('user_table.id'))

user = relationship("User", back_populates="addresses")

Base.metadata.create_all(engine) 

u1 = User(name = "bob")
u2 = User(name = "jan")
a1 = Email(email = "b...@school.nl", user = u1)
a2 = Email(email = "j...@school.nl", user = u2)
a3 = Email(email = "j...@home.nl", user = u2)

session = Session()
session.add_all([u1, u2, a1, a2, a3])
session.commit()
query = session.query(Email)
query = query.join("user") #or query = query.join("user", aliased = 
True)
query = query.add_columns(Email.email, User.name)
for r in query.all():
print r[1:],
print

and if i use the line:

query = query.join("user")

this results in:

  (u'b...@school.nl', u'bob') (u'j...@school.nl', u'jan') 
(u'j...@home.nl', u'jan')

which i would expect, but if i exchange the line with:

 query = query.join("user", aliased = True)

i get the full cross product between the tables:

 (u'b...@school.nl', u'bob') (u'j...@school.nl', u'bob') (u'j...@home.nl', 
u'bob') (u'b...@school.nl', u'jan') (u'j...@school.nl', u'jan') 
(u'j...@home.nl', u'jan')

Can anyone explain why this difference occurs?

Cheers, Lars

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Re: [sqlalchemy] label & column_descriptions

[lars van Gemerden]

[i]
  File "D:\Documents\Code\python\floware\models\flow\libraries\queries.py",
line 65, in __getitem__
return self._results_()[index]
  File "D:\Documents\Code\python\floware\models\flow\libraries\queries.py",
line 41, in _results_
self.refresh()
  File "D:\Documents\Code\python\floware\models\flow\libraries\queries.py",
line 51, in refresh
self.__results = self.all()
  File "D:\Documents\Code\python\floware\models\flow\libraries\queries.py",
line 70, in all
return self._query_.with_session(session).all()
  File "build\bdist.win32\egg\sqlalchemy\orm\query.py", line 2241, in all
return list(self)
  File "build\bdist.win32\egg\sqlalchemy\orm\loading.py", line 75, in
instances
labels) for row in fetch]
  File "build\bdist.win32\egg\sqlalchemy\orm\query.py", line 3209, in proc
return row[column]
InvalidRequestError: Ambiguous column name '"Persoon".naam' in result set!
try 'use_labels' option on select statement.



On Thu, Mar 20, 2014 at 4:28 PM, Michael Bayer wrote:

>
> On Mar 20, 2014, at 9:22 AM, lars van gemerden 
> wrote:
>
> > I solved it (again):
> >
> > for future reference:
> >
> > say you have the expression Person.name (Person is SQLA class) to use in
> a query, to have a label show up under that name in the resulting
> KeyedTuple's:
> >
> > to do:
> >
> > Person.name.label("something")
> >
> > is not enough, you have to do:
> >
> > expr = Person.name.label("something")
> >
> > and something like query.add_column(expr) after.
> >
> > Also Person.name.label("Person.name") and
>  Person.name.label("Person_name")give exceptions!
> >
> > (I am auto generating labels to use as column names on gui tables in a
> web page and guess which 2 i tried first :-)
>
>
> you can query for the label up front, query(Person.name.label('foo'))
>
> also what's the exception with those other labels?
>
> --
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-- 

Lars van Gemerden
l...@rational-it.com
+31 6 26 88 55 39


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[sqlalchemy] Re: label & column_descriptions

[lars van gemerden]

thanks, Michael,

we crossed responses; i thought it was something like that, but there are 
some gotchas (at least for me; see above).

CL

On Thursday, March 20, 2014 2:22:24 PM UTC+1, lars van gemerden wrote:
>
> I solved it (again):
>
> for future reference:
>
> say you have the expression Person.name (Person is SQLA class) to use in a 
> query, to have a label show up under that name in the resulting 
> KeyedTuple's:
>
> to do:
>
> Person.name.label("something") 
>
> is not enough, you have to do:
>
> expr = Person.name.label("something") 
>
> and something like query.add_column(expr) after.
>
> Also Person.name.label("Person.name") and 
>  Person.name.label("Person_name")give exceptions!
>
> (I am auto generating labels to use as column names on gui tables in a web 
> page and guess which 2 i tried first :-)
>
> Cheers, Lars
>

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[sqlalchemy] Re: label & column_descriptions

[lars van gemerden]

I solved it (again):

for future reference:

say you have the expression Person.name (Person is SQLA class) to use in a 
query, to have a label show up under that name in the resulting 
KeyedTuple's:

to do:

Person.name.label("something") 

is not enough, you have to do:

expr = Person.name.label("something") 

and something like query.add_column(expr) after.

Also Person.name.label("Person.name") and 
 Person.name.label("Person_name")give exceptions!

(I am auto generating labels to use as column names on gui tables in a web 
page and guess which 2 i tried first :-)

Cheers, Lars

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[sqlalchemy] label & column_descriptions

[lars van gemerden]

Hi all,

I solved this before, but i took me half a day and a lot of guessing and i 
forgot.

If i add (sometimes calculated) columns to a query and i want to set the 
names manually (via label()?), how do i do that? How will i make them show 
up in a resulting KeyedTuple/column_descriptions()?

Cheers, Lars

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Re: [sqlalchemy] AssertionError

[lars van gemerden]

clear and bug found .. thanks



On Tuesday, March 18, 2014 4:51:36 PM UTC+1, Michael Bayer wrote:
>
> it means this:
>
> a1 = A(id=1)
> session.add(a1)
> session.commit()
>
> a2 = A(id=1)
> session.add(a2)   # <— error
>
>
> On Mar 18, 2014, at 9:59 AM, lars van gemerden 
> > 
> wrote:
>
> Hi all,
>
> Does anyone know hoe to interpret the following error?
>
> AssertionError: A conflicting state is already present in the identity 
> map for key (, (1,))
>
> Cheers, Lars
>
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>
>
>

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[sqlalchemy] AssertionError

[lars van gemerden]

Hi all,

Does anyone know hoe to interpret the following error?

AssertionError: A conflicting state is already present in the identity 
map for key (, (1,))

Cheers, Lars

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Re: [sqlalchemy] StaleDataError/ObjectDeletedError

[lars van gemerden]

Ok, Michael,

That helped a lot, what i have done is (for future reference/others);

1) turned of autoflush on all sessions,
2) shortened the lifespan of session to a minimum,
3) removed the "if object_session(obj): session.merge(obj)" option in the 
Session() function,

This seems to have solved the problem for now (needs more testing)!

Thanks for the link to the talk as well.

Cheerio, Lars



On Saturday, February 1, 2014 4:34:10 PM UTC+1, Michael Bayer wrote:
>
>
> On Feb 1, 2014, at 9:01 AM, lars van gemerden 
> > 
> wrote: 
>
> > Oh, on more question: 
> > 
> > might there be anything inherently wrong with the scoped_session 
> approach that i showed in the code snippets above? 
>
> the code which illustrates the @contextmanager and the “def Session()” 
> looks error-prone and entirely awkward, and the rationale for such a 
> context manager isn’t apparent.   
>
> It appears to be mixing the intent of wishing to share random rows between 
> multiple sessions (a bad idea) while at the same time trying to conceal the 
> details of how a delicate operation like that is performed (it guesses 
> whether add() or merge() should be used, etc).  It also seems to mix the 
> concerns of dealing with object mechanics and session creation at the same 
> time which are typically two different concerns, not to mention that it has 
> a complex system of committing or not committing using flags which makes it 
> unsurprising that you’re seeing non-existent rows show up in other 
> transactions. 
>
> So yeah, if it were me, I’d definitely try to approach whatever the 
> problem is it’s trying to solve in a different way, one which preferably 
> sticks to the patterns outlined in the ORM tutorial as much as possible 
> (e.g. one session at a time, load/manipulate objects, commit(), throw 
> everything away).   Those points at which an application actually uses two 
> sessions at once, or transfers objects between them, should be very 
> isolated cases with very explicit mechanics and clear rationale why this 
> operation is needed in this specific case (where typical cases are: sending 
> objects into worker threads or processes, moving objects in and out of 
> caching layers, or running two transactions simultaneously so that one can 
> commit and the other roll back, such as a transaction writing to an 
> application history table).The app wouldn’t have a generic “here’s one 
> of those places we need to use two sessions with a specific target object 
> to pull out of one of them” use case such that a context manager is needed, 
> there should be extremely few places where that kind of thing goes on. 
>
> The kind of issue you’re hitting is exactly the one I talk about in detail 
> in my talk, “The SQLAlchemy Session in Depth”: 
> http://techspot.zzzeek.org/2012/11/14/pycon-canada-the-sqlalchemy-session-in-depth/
>  Page 18 of the PDF illustrates a slide “Lack of Behavioral Constraints 
> Creates Confusion” illustrating an anti-pattern similar to the one I think 
> we’re seeing here. 
>
>

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Re: [sqlalchemy] StaleDataError/ObjectDeletedError

[lars van gemerden]

Oh, on more question:

might there be anything inherently wrong with the scoped_session approach 
that i showed in the code snippets above?

CL

On Saturday, February 1, 2014 1:25:27 PM UTC+1, lars van gemerden wrote:
>
> Thanks, this helps some to narrow it down.
>
> Trying to zoom in:
>
> - why would sqla try to UPDATE (instead of INSERT) a row in the database, 
> when the row/object was never committed before?
> - when you flush an object to the database and then close the session that 
> flushed (no commit), what happens to the flushed data?
> - if an object is in a session and it has_identity, why would accessing 
> obj.id (id is the primary key) fail (see above)? 
> - Is there (in principle) a problem with:
>  + having an object of a mapped class which was never committed 
> (but maybe was added to a session and flushed, after which the session was 
> closed)
>  + setting an attribute of that object with another object that 
> was queried from the database
>  + committing the first object to the database?
>
> Cheers, Lars
>
> On Saturday, February 1, 2014 3:42:09 AM UTC+1, Michael Bayer wrote:
>>
>>
>> On Jan 31, 2014, at 8:11 PM, lars van gemerden  
>> wrote:
>>
>>
>> "this means an object was meant to be UPDATEed via the ORM, however the 
>> row which is the target of the UPDATE is missing.  Either the primary key 
>> of this row changed somehow, or the row was deleted, *or* the row is not 
>> visible to your transaction (this seems to be your case)."
>>
>> -  could the error also occur when the object was never committed to the 
>> database (which seems to be the case; the commit where the error occurs 
>> should be the first time the Company object is committed to the database)?
>>
>>
>> sure
>>
>> -  this seems to suggest that it is possible that a row is in the 
>> database, but that it is not visible to a transaction; is that possible?
>>
>>
>> absolutely, the link http://en.wikipedia.org/wiki/Transaction_isolation is 
>> relevant here
>>
>>
>>

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Re: [sqlalchemy] StaleDataError/ObjectDeletedError

[lars van gemerden]

Thanks, this helps some to narrow it down.

Trying to zoom in:

- why would sqla try to UPDATE (instead of INSERT) a row in the database, 
when the row/object was never committed before?
- when you flush an object to the database and then close the session that 
flushed (no commit), what happens to the flushed data?
- if an object is in a session and it has_identity, why would accessing 
obj.id (id is the primary key) fail (see above)? 
- Is there (in principle) a problem with:
 + having an object of a mapped class which was never committed 
(but maybe was added to a session and flushed, after which the session was 
closed)
 + setting an attribute of that object with another object that was 
queried from the database
 + committing the first object to the database?

Cheers, Lars

On Saturday, February 1, 2014 3:42:09 AM UTC+1, Michael Bayer wrote:
>
>
> On Jan 31, 2014, at 8:11 PM, lars van gemerden 
> > 
> wrote:
>
>
> "this means an object was meant to be UPDATEed via the ORM, however the 
> row which is the target of the UPDATE is missing.  Either the primary key 
> of this row changed somehow, or the row was deleted, *or* the row is not 
> visible to your transaction (this seems to be your case)."
>
> -  could the error also occur when the object was never committed to the 
> database (which seems to be the case; the commit where the error occurs 
> should be the first time the Company object is committed to the database)?
>
>
> sure
>
> -  this seems to suggest that it is possible that a row is in the 
> database, but that it is not visible to a transaction; is that possible?
>
>
> absolutely, the link http://en.wikipedia.org/wiki/Transaction_isolation is 
> relevant here
>
>
>

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Re: [sqlalchemy] StaleDataError/ObjectDeletedError

[lars van gemerden]

Hi Michael,

With some more detail:

What i do is:
1 make a new object (mapped)-> obj1
2 create a scoped session (with context manager)-> session1
3 do session1.add(obj) 
4 create another scoped session -> session2 
5 do session2.query(someclass).get(some_id)->obj2 
6 close session2, no commit, no flush -> obj2 is detached (right?)
7 do obj1.someattr.append(obj2)
8 do session1.commit()
9 get the first ERROR above 

basically i use

def Session( objs):
session = session_maker()
for obj in objs:
if object_session(obj) is None:
session.add(obj)
else:
session.merge(obj)
return session

@contextmanager
def scoped_session(objs = [], commit = True):
session = Session(objs)
try:
yield session
if commit:
session.commit()
except:
session.rollback()
raise
finally:
session.close()

and essentially code description (1-8) above comes down to:

obj1 = cls1()

with scoped_session([obj1]) as session1:
obj1.somefield = "somevalue"
with scoped_session(commit = False) as session2:
obj2 = session2.query(cls2).get(some_id)
obj1.someattr.append(obj2)

if i just do:

with scoped_session([obj1]) as session1:
obj1.somefield = "somevalue"

there is no problem.

Also:

"this means an object was meant to be UPDATEed via the ORM, however the row 
which is the target of the UPDATE is missing.  Either the primary key of 
this row changed somehow, or the row was deleted, *or* the row is not 
visible to your transaction (this seems to be your case)."

-  could the error also occur when the object was never committed to the 
database (which seems to be the case; the commit where the error occurs 
should be the first time the Company object is committed to the database)?
-  this seems to suggest that it is possible that a row is in the database, 
but that it is not visible to a transaction; is that possible?

As far as i know in the code that causes the problem, i do not do any 
deletes and i do not call flush myself.

Doing some more testing, now i get more of the second error in:

def __str__(self): #in mapped class
print object_session(self) is not None, has_identity(self) # True, 
True, <= OK
print self.id #<= ERROR
..

with trace:
File "d:\Documents\Code\python\floware\models\flow\processes.py", line 333, 
in run
  self.execute(input, output)
File "d:\Documents\Code\python\floware\toolshed\logs.py", line 55, in 
wrapper
  f_result = func(*v, **k)
File "d:\Documents\Code\python\floware\models\flow\libraries\basic.py", 
line 159, in execute
  print "%s %s" % (self.cursor, str(i.item))
File "d:\Documents\Code\python\floware\models\data\database.py", line 281, 
in __str__
  print object_session(self), has_identity(self), self.id
File 
"C:\python27\lib\site-packages\sqlalchemy-0.8.3-py2.7-win32.egg\sqlalchemy\orm\attributes.py",
 
line 316, in __get__
File 
"C:\python27\lib\site-packages\sqlalchemy-0.8.3-py2.7-win32.egg\sqlalchemy\orm\attributes.py",
 
line 611, in get
File 
"C:\python27\lib\site-packages\sqlalchemy-0.8.3-py2.7-win32.egg\sqlalchemy\orm\state.py",
 
line 380, in __call__
File 
"C:\python27\lib\site-packages\sqlalchemy-0.8.3-py2.7-win32.egg\sqlalchemy\orm\loading.py",
 
line 606, in load_scalar_attributes

sqlalchemy.orm.exc.ObjectDeletedError: Instance '' 
has been deleted, or its row is otherwise not present.

CL

>
>

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[sqlalchemy] StaleDataError/ObjectDeletedError

[lars van gemerden]

Hi, all

I am running into these 2 errors and have run out of ideas what to do about 
it (also because i don't what they mean); They seem to happen in exactly 
the same circumstances.

Traceback (most recent call last):
  File "C:\python27\lib\site-packages\bottle.py", line 781, in _handle
return route.call(**args)
  File "C:\python27\lib\site-packages\bottle.py", line 1592, in wrapper
rv = callback(*a, **ka)
  File "d:\Documents\Code\python\floware\server\webserver.py", line 202, in 
post_task
task.from_json(request.json, path = pathlist([task._id_]))
  File "C:\python27\lib\contextlib.py", line 24, in __exit__
self.gen.next()
  File "d:\Documents\Code\python\floware\models\flow\tasks.py", line 55, in 
scoped_session
session.commit()
  File "build\bdist.win32\egg\sqlalchemy\orm\session.py", line 721, in 
commit
self.transaction.commit()
  File "build\bdist.win32\egg\sqlalchemy\orm\session.py", line 354, in 
commit
self._prepare_impl()
  File "build\bdist.win32\egg\sqlalchemy\orm\session.py", line 334, in 
_prepare_impl
self.session.flush()
  File "build\bdist.win32\egg\sqlalchemy\orm\session.py", line 1818, in 
flush
self._flush(objects)
  File "build\bdist.win32\egg\sqlalchemy\orm\session.py", line 1936, in 
_flush
transaction.rollback(_capture_exception=True)
  File "build\bdist.win32\egg\sqlalchemy\util\langhelpers.py", line 58, in 
__exit__
compat.reraise(exc_type, exc_value, exc_tb)
  File "build\bdist.win32\egg\sqlalchemy\orm\session.py", line 1900, in 
_flush
flush_context.execute()
  File "build\bdist.win32\egg\sqlalchemy\orm\unitofwork.py", line 372, in 
execute
rec.execute(self)
  File "build\bdist.win32\egg\sqlalchemy\orm\unitofwork.py", line 525, in 
execute
uow
  File "build\bdist.win32\egg\sqlalchemy\orm\persistence.py", line 59, in 
save_obj
mapper, table, update)
  File "build\bdist.win32\egg\sqlalchemy\orm\persistence.py", line 514, in 
_emit_update_statements
(table.description, len(update), rows))
StaleDataError: UPDATE statement on table 'Company' expected to update 1 
row(s); 0 were matched.

OR

File "d:\Documents\Code\python\floware\models\flow\processes.py", line 333, 
in run
  self.execute(input, output)
File "d:\Documents\Code\python\floware\toolshed\logs.py", line 55, in 
wrapper
  f_result = func(*v, **k)
File "d:\Documents\Code\python\floware\models\flow\libraries\basic.py", 
line 159, in execute
  print "%s %s" % (self.cursor, str(i.item))
File "d:\Documents\Code\python\floware\models\data\database.py", line 282, 
in __str__
  return '{%s-> %s}' %(type(self).__name__, ', '.join(['%s: %s' % (str(k), 
repr(getattr(self, k))) for k in self._entity_]))
File 
"C:\python27\lib\site-packages\sqlalchemy-0.8.3-py2.7-win32.egg\sqlalchemy\orm\attributes.py",
 
line 316, in __get__
File 
"C:\python27\lib\site-packages\sqlalchemy-0.8.3-py2.7-win32.egg\sqlalchemy\orm\attributes.py",
 
line 611, in get
File 
"C:\python27\lib\site-packages\sqlalchemy-0.8.3-py2.7-win32.egg\sqlalchemy\orm\state.py",
 
line 380, in __call__
File 
"C:\python27\lib\site-packages\sqlalchemy-0.8.3-py2.7-win32.egg\sqlalchemy\orm\loading.py",
 
line 606, in load_scalar_attributes
sqlalchemy.orm.exc.ObjectDeletedError: Instance '' 
has been deleted, or its row is otherwise not present.

What i do is:
1 make a new object (mapped)-> obj1
2 add it to a session -> session1 
3 start another session -> session2 
4 do a get(id) on session2 (which should result in access to the database, 
since i just started the session) -> obj2 
5 close session2
6 do obj1.someattr.append(obj2)
7 do session1.commit()
8 get the first ERROR above 

OR
9 close session1
10 add obj1 to another session -> session3
11 do the returnb the string from __str__: return '{%s-> %s}' 
%(type(self).__name__, ', '.join(['%s: %s' % (str(k), repr(getattr(self, 
k))) for k in self._entity_])) (see stacktrace)
12 get the second ERROR above

I think thats all that could be relevant; if i don't do steps 3-6 there is 
no problem!

Can anyone point me in the right direction of what this error might mean, 
how to find the error or how to solve the problem?

Why would the first error not occur in all cases?

Cheers, Lars

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[sqlalchemy] Re: keyword search

[lars van gemerden]

PS: a search over all fields would be great too!

On Tuesday, December 17, 2013 11:01:51 AM UTC+1, lars van gemerden wrote:
>
> Hi all,
>
> I want to implement a keyword search over multiple fields and/or even 
> related tables. Tables/orm classes are not designed by me but by users of 
> my software, so i will probably let them indicate whether a 
> field/relationship should be included (or I'll base it on type, e.g. String 
> and Text fields only).
>
> I was thinking of using a hybrid property, but they seem a bit to magical 
> for this purpose (might be really slow). Is there a best practice/standard 
> way to do this in SQLA?
>
> Cheers, Lars
>

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[sqlalchemy] keyword search

[lars van gemerden]

Hi all,

I want to implement a keyword search over multiple fields and/or even 
related tables. Tables/orm classes are not designed by me but by users of 
my software, so i will probably let them indicate whether a 
field/relationship should be included (or I'll base it on type, e.g. String 
and Text fields only).

I was thinking of using a hybrid property, but they seem a bit to magical 
for this purpose (might be really slow). Is there a best practice/standard 
way to do this in SQLA?

Cheers, Lars

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Re: [sqlalchemy] nullable/association question

[lars van gemerden]

in my application the query for roles is practically impossible to get into 
the block (close to) where the user instance is created, i could not attach 
the User instance to a session at all (before being ready to commit), but 
would i still be able to set the roles on the User?

CL

On Thursday, November 21, 2013 3:57:44 PM UTC+1, Michael Bayer wrote:
>
> I’d stick with judicious use of “with session.no_autoflush:" around the 
> block where the User is being constructed and isn’t ready to flush yet.
>
>
> On Nov 21, 2013, at 6:29 AM, lars van Gemerden 
> > 
> wrote:
>
> Hi Michael,
>
> since i might also start with a Role instance and add User instances to 
> them i need a symmetrical solution with regard ref and backref (and i think  
> casade_backrefs=False 
> would not work in that case?).
>
> So i tested two solutions which both seem to work in this specific case:
>
>  - create a separate session for the query on Role 
> (session.query(Role).all()); not the same session the User instance is in 
> (as i did before)
>  - set autoflush to false on the query as in 
> (session.query(Role).autoflush(False).all())
>
> Since you did not mention the second solution, i wondered whether there 
> are possible disadvantages to the second approach; the first one seems 
> slower but cleaner.
>
> Cheers, Lars
>
>
> On Wed, Nov 20, 2013 at 4:51 PM, Michael Bayer 
> 
> > wrote:
>
>> you either want to prevent User from being cascaded and/or added into the 
>> Session ahead of time, which if this is occurring via backref you might 
>> want to look at casade_backrefs=False (
>> http://docs.sqlalchemy.org/en/rel_0_9/orm/session.html?highlight=cascade_backrefs#controlling-cascade-on-backrefs).
>>  
>>  If not that, then use “with session.no_autoflush” for the period of 
>> time that you query for Role.
>>
>>
>>
>>
>> On Nov 20, 2013, at 8:02 AM, lars van gemerden 
>> > 
>> wrote:
>>
>> Hi all,
>>
>> I have 2 sqla classes with mapped tables: User and Role with a many to 
>> many relationship (User.roles/Role.users) through an association table. 
>> User has columns email and password, both non nullable.
>>
>> I create an instance of User but do not commit it yet, next i do a query 
>> on Role: session.query(Role).all() (to be able to let an end-user choose 
>> one or more roles for the for the newly created User).
>>
>> This gives the error: IntegrityError: (IntegrityError) User.email may not 
>> be NULL u'INSERT INTO "User" (_created_, discriminator, email, password) 
>> VALUES (CURRENT_TIMESTAMP, ?, ?, ?)' (None, None, None)
>>
>> I think the query tries to flush the instance of User, which causes the 
>> error.
>>
>> My questions is: Why and how do i avoid it? I just want a list of all 
>> roles currently in the Role table to be able to assign one or moe to the 
>> User instance.
>>
>> Cheers, Lars
>>
>>
>>
>> -- 
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>>
>>
>>
>
>
> -- 
> 
> Lars van Gemerden
> la...@rational-it.com 
> +31 6 26 88 55 39
>  
>
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>
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Re: [sqlalchemy] just a picture

[Lars van Gemerden]

The tool


Lars van Gemerden
l...@rational-it.com
+31 6 26 88 55 39


> On 21 nov. 2013, at 15:02, Stefane Fermigier  wrote:
> 
> Hi Lars,
> 
> Are you working on the tool, or on the application whose schema is depicted 
> on the tool ?
> 
> Regards,
> 
>   S.
> 
>> On Nov 21, 2013, at 1:38 PM, lars van gemerden wrote:
>> 
>> something i have been working on, running on sqlalchemy .
>> 
>> 
>> 
>> Cheers, Lars
>> 
>> -- 
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> 
> Stefane Fermigier - http://fermigier.com/ - http://twitter.com/sfermigier - 
> http://linkedin.com/in/sfermigier
> Founder & CEO, Abilian - Enterprise Social Software - http://www.abilian.com/
> Co-Founder and Chairman, Systematic Free&OSS Special Interest Group - 
> http://www.gt-logiciel-libre.org/
> Co-Founder & Vice-President, National Council for Free&OSS - http://cnll.fr/
> Vice President, Open World Forum 2013 - http://openworldforum.org/
> "Well done is better than well said." - Benjamin Franklin
> "There's no such thing as can't. You always have a choice." - Ken Gor
> "Le vrai courage, c'est de faire ce qui est juste." - Dr Benjamin Justice
> 
> 
> 
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Re: [sqlalchemy] just a picture

[Lars van Gemerden]

No, sorry, to be able to do this, a lot of of settings are predetermined (the 
modeller can set nullable, unique, validation, etc, but not settings like 
cascades). The goal is to make a modelling tool that can run on existing db 
engines and persist python objects representing 'business' data, not to be a 
modelling tool with the reach of sqla itself.

Cheers, Lars

========
Lars van Gemerden
l...@rational-it.com
+31 6 26 88 55 39


> On 21 nov. 2013, at 15:19, Werner  wrote:
> 
>> On 21/11/2013 15:02, Stefane Fermigier wrote:
>> Hi Lars,
>> 
>> Are you working on the tool, or on the application whose schema is depicted 
>> on the tool ?
> Assuming it is a tool this would be very nice.
> 
> Can it read an existing SA model?
> 
> Werner
> 
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[sqlalchemy] just a picture

[lars van gemerden]

something i have been working on, running on sqlalchemy .


Cheers, Lars

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Re: [sqlalchemy] nullable/association question

[lars van Gemerden]

Hi Michael,

since i might also start with a Role instance and add User instances to
them i need a symmetrical solution with regard ref and backref (and i
think  casade_backrefs=False
would not work in that case?).

So i tested two solutions which both seem to work in this specific case:

 - create a separate session for the query on Role
(session.query(Role).all()); not the same session the User instance is in
(as i did before)
 - set autoflush to false on the query as in
(session.query(Role).autoflush(False).all())

Since you did not mention the second solution, i wondered whether there are
possible disadvantages to the second approach; the first one seems slower
but cleaner.

Cheers, Lars


On Wed, Nov 20, 2013 at 4:51 PM, Michael Bayer wrote:

> you either want to prevent User from being cascaded and/or added into the
> Session ahead of time, which if this is occurring via backref you might
> want to look at casade_backrefs=False (
> http://docs.sqlalchemy.org/en/rel_0_9/orm/session.html?highlight=cascade_backrefs#controlling-cascade-on-backrefs).
>  If not that, then use “with session.no_autoflush” for the period of
> time that you query for Role.
>
>
>
>
> On Nov 20, 2013, at 8:02 AM, lars van gemerden 
> wrote:
>
> Hi all,
>
> I have 2 sqla classes with mapped tables: User and Role with a many to
> many relationship (User.roles/Role.users) through an association table.
> User has columns email and password, both non nullable.
>
> I create an instance of User but do not commit it yet, next i do a query
> on Role: session.query(Role).all() (to be able to let an end-user choose
> one or more roles for the for the newly created User).
>
> This gives the error: IntegrityError: (IntegrityError) User.email may not
> be NULL u'INSERT INTO "User" (_created_, discriminator, email, password)
> VALUES (CURRENT_TIMESTAMP, ?, ?, ?)' (None, None, None)
>
> I think the query tries to flush the instance of User, which causes the
> error.
>
> My questions is: Why and how do i avoid it? I just want a list of all
> roles currently in the Role table to be able to assign one or moe to the
> User instance.
>
> Cheers, Lars
>
>
>
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[sqlalchemy] nullable/association question

[lars van gemerden]

Hi all,

I have 2 sqla classes with mapped tables: User and Role with a many to many 
relationship (User.roles/Role.users) through an association table. User has 
columns email and password, both non nullable.

I create an instance of User but do not commit it yet, next i do a query on 
Role: session.query(Role).all() (to be able to let an end-user choose one 
or more roles for the for the newly created User).

This gives the error: IntegrityError: (IntegrityError) User.email may not 
be NULL u'INSERT INTO "User" (_created_, discriminator, email, password) 
VALUES (CURRENT_TIMESTAMP, ?, ?, ?)' (None, None, None)

I think the query tries to flush the instance of User, which causes the 
error.

My questions is: Why and how do i avoid it? I just want a list of all roles 
currently in the Role table to be able to assign one or moe to the User 
instance.

Cheers, Lars


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Re: [sqlalchemy] quick query question

[Lars van Gemerden]

Thanks again ..


Lars van Gemerden
l...@rational-it.com
+31 6 26 88 55 39


> On 28 okt. 2013, at 18:12, Michael Bayer  wrote:
> 
> the list of objects are for when the query is set to return exactly one 
> mapped class.  query.column_descriptions will show this.
> 
> 
>> On Oct 28, 2013, at 12:44 PM, lars van gemerden  wrote:
>> 
>> Hi,
>> 
>> Short question: when does e.g. query.all() returns a list of objects and 
>> when it returns a list of NamedTuple's?
>> 
>> is it only after you call add_columns() on the query that all() starts 
>> returning NamedTuple's? 
>> 
>> Cheers, Lars
>> 
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[sqlalchemy] quick query question

[lars van gemerden]

Hi,

Short question: when does e.g. query.all() returns a list of objects and 
when it returns a list of NamedTuple's?

is it only after you call add_columns() on the query that all() starts 
returning NamedTuple's? 

Cheers, Lars

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Re: [sqlalchemy] quelified/disambiguated column names in query

[lars van Gemerden]

Thank you,

i must have blundered over that in the docs ...

Lars


On Mon, Oct 21, 2013 at 11:36 PM, Michael Bayer wrote:

>
> On Oct 21, 2013, at 5:20 PM, lars van gemerden 
> wrote:
>
> Hello,
>
> Say that i have a table with reports with a column 'title' and a one to
> many relationship 'chapters' to chapters also with a column 'title', if i
> join these tables in a query, like:
>
> q =
> self.session.query(Report).join(Report.chapters).add_columns(Report.title,
> Chapter.title, Chapter.text)
> for p in q.all():
> print p.title
>
> print p.title prints the title of the chapter.
>
> Is there a way to let the query.all() return NamedTuples with
> qualified/disambiguated  names (either 'title' and 'chapters.title' or
> 'Report.title' and 'Chapter.title' or perhaps with underscores), because
> now i see no way to distinguish the columns (apart maybe from the order).
>
> p.keys() returns 'title' twice.
>
>
> use labels:
>
> add_columns(Report.title.label("report_title"),
> Chapter.title.label("chapter_title"))
>
>
>
>
>
> Cheers, Lars
>
> PS: i am using sqla 0.7.5
>
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[sqlalchemy] quelified/disambiguated column names in query

[lars van gemerden]

Hello,

Say that i have a table with reports with a column 'title' and a one to 
many relationship 'chapters' to chapters also with a column 'title', if i 
join these tables in a query, like:

q = 
self.session.query(Report).join(Report.chapters).add_columns(Report.title, 
Chapter.title, Chapter.text)
for p in q.all():
print p.title

print p.title prints the title of the chapter.

Is there a way to let the query.all() return NamedTuples with 
qualified/disambiguated  names (either 'title' and 'chapters.title' or 
'Report.title' and 'Chapter.title' or perhaps with underscores), because 
now i see no way to distinguish the columns (apart maybe from the order).

p.keys() returns 'title' twice.

Cheers, Lars

PS: i am using sqla 0.7.5

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Re: [sqlalchemy] query question

[lars van Gemerden]

OK, never mind |-)

should be:

   q = q.with_entities(Report.number)
   q = q.add_columns(Report.number)

sry



On Mon, Sep 9, 2013 at 2:43 PM, lars van gemerden wrote:

> Ok, i've tried both (and each separately), as in:
>
> r1 = Report(number = 1, title = "The Bird")
> r2 = Report(number = 2, title = "The Bucket")
> session.add_all([r1, r2])
> session.commit()
> q = self.session.query(Report.title)
> q.with_entities(Report.number)
> q.add_columns(Report.number)
> print q.all()
>
> printing:
>
> [(u'The Bird',), (u'The Bucket',)]
>
> what i would like to see is:
>
>[(u'The Bird', 1), (u'The Bucket', 2)]
>
> or something similar.
>
> Cheers, Lars
>
> On Wednesday, September 4, 2013 1:24:28 PM UTC+2, Simon King wrote:
>
>> On Wed, Sep 4, 2013 at 12:05 PM, lars van gemerden 
>> wrote:
>> > I  think i must be reading over something, but:
>> >
>> > is there a way to delay the selection of attributes in a query;
>> something
>> > like
>> >
>> >  >>> session.query(Person).filter(**Person.age >
>> > 100).select(Person.name).**first()
>> >
>> >  >>>  (u"Ancient Bob",)
>> >
>>
>> I'm not sure quite what you mean, but the with_entities method of
>> Query would seem to be the closest to your example:
>>
>>   http://docs.sqlalchemy.org/en/**rel_0_8/orm/query.html#**
>> sqlalchemy.orm.query.Query.**with_entities<http://docs.sqlalchemy.org/en/rel_0_8/orm/query.html#sqlalchemy.orm.query.Query.with_entities>
>>
>> I assume you know you can also do this:
>>
>>   session.query(Person.name).**filter(Person.age > 100).first()
>>
>> You can also defer certain columns so that they will be loaded lazily:
>>
>>   http://docs.sqlalchemy.org/en/**rel_0_8/orm/mapper_config.**
>> html#deferred-column-loading<http://docs.sqlalchemy.org/en/rel_0_8/orm/mapper_config.html#deferred-column-loading>
>>
>> Hope that helps,
>>
>> Simon
>>
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Re: [sqlalchemy] query question

[lars van gemerden]

Ok, i've tried both (and each separately), as in:

r1 = Report(number = 1, title = "The Bird") 
r2 = Report(number = 2, title = "The Bucket")
session.add_all([r1, r2])
session.commit()
q = self.session.query(Report.title)
q.with_entities(Report.number)
q.add_columns(Report.number)
print q.all()

printing:

[(u'The Bird',), (u'The Bucket',)]

what i would like to see is:

   [(u'The Bird', 1), (u'The Bucket', 2)]
 
or something similar.

Cheers, Lars

On Wednesday, September 4, 2013 1:24:28 PM UTC+2, Simon King wrote:
>
> On Wed, Sep 4, 2013 at 12:05 PM, lars van gemerden 
> > 
> wrote: 
> > I  think i must be reading over something, but: 
> > 
> > is there a way to delay the selection of attributes in a query; 
> something 
> > like 
> > 
> >  >>> session.query(Person).filter(Person.age > 
> > 100).select(Person.name).first() 
> > 
> >  >>>  (u"Ancient Bob",) 
> > 
>
> I'm not sure quite what you mean, but the with_entities method of 
> Query would seem to be the closest to your example: 
>
>   
> http://docs.sqlalchemy.org/en/rel_0_8/orm/query.html#sqlalchemy.orm.query.Query.with_entities
>  
>
> I assume you know you can also do this: 
>
>   session.query(Person.name).filter(Person.age > 100).first() 
>
> You can also defer certain columns so that they will be loaded lazily: 
>
>   
> http://docs.sqlalchemy.org/en/rel_0_8/orm/mapper_config.html#deferred-column-loading
>  
>
> Hope that helps, 
>
> Simon 
>

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[sqlalchemy] query question

[lars van gemerden]

I  think i must be reading over something, but:

is there a way to delay the selection of attributes in a query; something 
like

 >>> session.query(Person).filter(Person.age > 
100).select(Person.name).first()

 >>>  (u"Ancient Bob",)

Cheers, Lars

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Re: [sqlalchemy] error related to setting attribute to same value twice

[lars van Gemerden]

My version is 0.7.5 (thought i was on 8 already), i will look at updating!

The error sounds similar, I'll get back on this after i do (after some
research to find out if updating is a good idea right now)

Cheers, Lars




On Tue, Sep 3, 2013 at 11:38 AM, Simon King  wrote:

> I realised after I sent that script that I wasn't reproducing quite
> the same situation. I should have loaded the person from the database
> in sess2 as well, before trying to add the instance from sess1. In
> other words, change the end of the test script to say:
>
> sess2 = Session()
> dupe = sess2.query(Person).first()
> sess2.add(person)
> sess2.commit()
>
> So sess2 now contains an instance representing that database row. The
> error message is now:
>
> AssertionError: A conflicting state is already present in the identity
> map for key (, (1,))
>
> ...which is still not quite the same as your error message. What
> version of SQLAlchemy are you using? (The above was from 0.8.2)
>
> Simon
>
> On Tue, Sep 3, 2013 at 10:15 AM, lars van gemerden 
> wrote:
> > I am getting that same error (not the original one). For the moment i've
> > solved the problem in a different way, but it might pop up again. I'll
> keep
> > merge in mind (i've run into the" is already attached to session"
> before).
> >
> > Thank you, Lars
> >
> >
> > On Monday, September 2, 2013 9:18:11 PM UTC+2, Simon King wrote:
> >>
> >> Dunno, let's try it:
> >>
> >> import sqlalchemy as sa
> >> import sqlalchemy.orm as saorm
> >> from sqlalchemy.ext.declarative import declarative_base
> >>
> >> Base = declarative_base()
> >>
> >> class Person(Base):
> >> __tablename__ = 'people'
> >> id = sa.Column(sa.Integer, primary_key=True, autoincrement=True)
> >> name = sa.Column(sa.String(20))
> >>
> >> if __name__ == '__main__':
> >> engine = sa.create_engine('sqlite:///:memory:')
> >> Base.metadata.create_all(engine)
> >> Session = saorm.sessionmaker(bind=engine)
> >>
> >> # Create our first session and use it to add a Person to the
> database
> >> sess1 = Session()
> >> sess1.add(Person(name='lars'))
> >> sess1.commit()
> >> sess1.close()
> >>
> >> # Retrieve our Person from the database again.
> >> person = sess1.query(Person).first()
> >>
> >> # Now try to add that instance to a second session
> >> sess2 = Session()
> >> sess2.add(person)
> >> sess2.commit()
> >>
> >>
> >> Output:
> >>
> >> Traceback (most recent call last):
> >>...
> >> sqlalchemy.exc.InvalidRequestError: Object '' is
> >> already attached to session '1' (this is '2')
> >>
> >> Looks very similar to your error message. I'm using SA 0.8.0 - it looks
> >> like the message is slightly different in your version.
> >>
> >> The correct thing to do in this case is to use "session.merge" to
> create a
> >> copy of the object, attached to the new session. If you change the last
> few
> >> lines of the script above to:
> >>
> >> sess2 = Session()
> >> merged = sess2.merge(person)
> >> sess2.add(merged)
> >>
> >> ...it works fine.
> >>
> >> Hope that helps,
> >>
> >> Simon
> >>
> >> On 2 Sep 2013, at 19:58, lars van Gemerden 
> wrote:
> >>
> >> > Yes I know the question was a bit vague, but i couldn't think of a
> >> > simple way to show some code. A test case would probably require some
> major
> >> > surgery; I'll consider it though.
> >> >
> >> > It is possible that the second instance is associated with a different
> >> > session, i'd have to check. What actually happens if you add the same
> >> > instance to a second session?
> >> >
> >> > CL
> >> >
> >> >
> >> > On Mon, Sep 2, 2013 at 8:23 PM, Simon King 
> >> > wrote:
> >> > Without knowing your application it's very difficult to know...
> >> >
> >> > Is there any chance that the second object is already associated with
> a
> >> > different session? Perhaps from a different thread, or retrieved from
> a
> >> > cache or something

Re: [sqlalchemy] error related to setting attribute to same value twice

[lars van gemerden]

I am getting that same error (not the original one). For the moment i've 
solved the problem in a different way, but it might pop up again. I'll keep 
merge in mind (i've run into the" is already attached to session" before).

Thank you, Lars 

On Monday, September 2, 2013 9:18:11 PM UTC+2, Simon King wrote:
>
> Dunno, let's try it: 
>
> import sqlalchemy as sa 
> import sqlalchemy.orm as saorm 
> from sqlalchemy.ext.declarative import declarative_base 
>
> Base = declarative_base() 
>
> class Person(Base): 
> __tablename__ = 'people' 
> id = sa.Column(sa.Integer, primary_key=True, autoincrement=True) 
> name = sa.Column(sa.String(20)) 
>
> if __name__ == '__main__': 
> engine = sa.create_engine('sqlite:///:memory:') 
> Base.metadata.create_all(engine) 
> Session = saorm.sessionmaker(bind=engine) 
>
> # Create our first session and use it to add a Person to the database 
> sess1 = Session() 
> sess1.add(Person(name='lars')) 
> sess1.commit() 
> sess1.close() 
>
> # Retrieve our Person from the database again. 
> person = sess1.query(Person).first() 
>
> # Now try to add that instance to a second session 
> sess2 = Session() 
> sess2.add(person) 
> sess2.commit() 
>
>
> Output: 
>
> Traceback (most recent call last): 
>... 
> sqlalchemy.exc.InvalidRequestError: Object '' is 
> already attached to session '1' (this is '2') 
>
> Looks very similar to your error message. I'm using SA 0.8.0 - it looks 
> like the message is slightly different in your version. 
>
> The correct thing to do in this case is to use "session.merge" to create a 
> copy of the object, attached to the new session. If you change the last few 
> lines of the script above to: 
>
> sess2 = Session() 
> merged = sess2.merge(person) 
> sess2.add(merged) 
>
> ...it works fine. 
>
> Hope that helps, 
>
> Simon 
>
> On 2 Sep 2013, at 19:58, lars van Gemerden 
> > 
> wrote: 
>
> > Yes I know the question was a bit vague, but i couldn't think of a 
> simple way to show some code. A test case would probably require some major 
> surgery; I'll consider it though. 
> > 
> > It is possible that the second instance is associated with a different 
> session, i'd have to check. What actually happens if you add the same 
> instance to a second session? 
> > 
> > CL 
> > 
> > 
> > On Mon, Sep 2, 2013 at 8:23 PM, Simon King 
> > > 
> wrote: 
> > Without knowing your application it's very difficult to know... 
> > 
> > Is there any chance that the second object is already associated with a 
> different session? Perhaps from a different thread, or retrieved from a 
> cache or something similar? 
> > 
> > Producing a standalone test script would help in diagnosing the problem. 
> > 
> > Simon 
> > 
> > 
> > On 2 Sep 2013, at 18:56, Lars van Gemerden 
> > > 
> wrote: 
> > 
> > > Well, from the message yes, but i am not setting any primary keys 
> manually, so where could the second instance come from? 
> > > 
> > > CL 
> > > 
> > >  
> > > Lars van Gemerden 
> > > la...@rational-it.com  
> > > +31 6 26 88 55 39 
> > >  
> > > 
> > > On 2 sep. 2013, at 17:39, Simon King 
> > > > 
> wrote: 
> > > 
> > >> On Mon, Sep 2, 2013 at 4:01 PM, lars van gemerden <
> la...@rational-it.com > wrote: 
> > >>> Hi all, 
> > >>> 
> > >>> I have a one-to-one and many-to-one relationship (with an 
> association table 
> > >>> in the middle; Report.author-assoctable-Person.reports; why the 
> table in the 
> > >>> middle, you might ask, well it's a long story) and i am setting the 
> author 
> > >>> on a specific Report twice to the same value. This gives the 
> following 
> > >>> error: 
> > >>> 
> > >>>  InvalidRequestError: Can't attach instance  0x36a9350>; 
> > >>> another instance with key (, 
> (2,)) is 
> > >>> already present in this session. 
> > >>> 
> > >>> The first time i set the author, it works and if i change the author 
> it 
> > >>> works as well. 
> > >>> 
> > >>> This seems i little strange to me, why not be ab

Re: [sqlalchemy] error related to setting attribute to same value twice

[lars van Gemerden]

Yes I know the question was a bit vague, but i couldn't think of a simple
way to show some code. A test case would probably require some major
surgery; I'll consider it though.

It is possible that the second instance is associated with a different
session, i'd have to check. What actually happens if you add the same
instance to a second session?

CL


On Mon, Sep 2, 2013 at 8:23 PM, Simon King  wrote:

> Without knowing your application it's very difficult to know...
>
> Is there any chance that the second object is already associated with a
> different session? Perhaps from a different thread, or retrieved from a
> cache or something similar?
>
> Producing a standalone test script would help in diagnosing the problem.
>
> Simon
>
>
> On 2 Sep 2013, at 18:56, Lars van Gemerden  wrote:
>
> > Well, from the message yes, but i am not setting any primary keys
> manually, so where could the second instance come from?
> >
> > CL
> >
> > 
> > Lars van Gemerden
> > l...@rational-it.com
> > +31 6 26 88 55 39
> > ========
> >
> > On 2 sep. 2013, at 17:39, Simon King  wrote:
> >
> >> On Mon, Sep 2, 2013 at 4:01 PM, lars van gemerden 
> wrote:
> >>> Hi all,
> >>>
> >>> I have a one-to-one and many-to-one relationship (with an association
> table
> >>> in the middle; Report.author-assoctable-Person.reports; why the table
> in the
> >>> middle, you might ask, well it's a long story) and i am setting the
> author
> >>> on a specific Report twice to the same value. This gives the following
> >>> error:
> >>>
> >>>  InvalidRequestError: Can't attach instance  0x36a9350>;
> >>> another instance with key (, (2,))
> is
> >>> already present in this session.
> >>>
> >>> The first time i set the author, it works and if i change the author it
> >>> works as well.
> >>>
> >>> This seems i little strange to me, why not be able to set the
> attribute to
> >>> the same value twice?
> >>>
> >>> Otherwise i have to check whether the new and old values are equal
> (which
> >>> through the peculiarties of my code is somewhat wastefull)
> >>>
> >>
> >> I think the message is actually telling you that you have 2 different
> >> instances of your "person" class with the same primary key. SQLAlchemy
> >> uses an identity map to ensure that a particular row in the database
> >> is only identified by a single instance within a particular session.
> >> If you violate that assumption (eg. by loading one instance of
> >> "person" from the database, then creating another instance and setting
> >> its primary key), you will get errors like this.
> >>
> >> Does that sound plausible?
> >>
> >> Simon
> >>
> >> --
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Re: [sqlalchemy] error related to setting attribute to same value twice

[Lars van Gemerden]

Well, from the message yes, but i am not setting any primary keys manually, so 
where could the second instance come from?

CL


Lars van Gemerden
l...@rational-it.com
+31 6 26 88 55 39


On 2 sep. 2013, at 17:39, Simon King  wrote:

> On Mon, Sep 2, 2013 at 4:01 PM, lars van gemerden  
> wrote:
>> Hi all,
>> 
>> I have a one-to-one and many-to-one relationship (with an association table
>> in the middle; Report.author-assoctable-Person.reports; why the table in the
>> middle, you might ask, well it's a long story) and i am setting the author
>> on a specific Report twice to the same value. This gives the following
>> error:
>> 
>>   InvalidRequestError: Can't attach instance ;
>> another instance with key (, (2,)) is
>> already present in this session.
>> 
>> The first time i set the author, it works and if i change the author it
>> works as well.
>> 
>> This seems i little strange to me, why not be able to set the attribute to
>> the same value twice?
>> 
>> Otherwise i have to check whether the new and old values are equal (which
>> through the peculiarties of my code is somewhat wastefull)
>> 
> 
> I think the message is actually telling you that you have 2 different
> instances of your "person" class with the same primary key. SQLAlchemy
> uses an identity map to ensure that a particular row in the database
> is only identified by a single instance within a particular session.
> If you violate that assumption (eg. by loading one instance of
> "person" from the database, then creating another instance and setting
> its primary key), you will get errors like this.
> 
> Does that sound plausible?
> 
> Simon
> 
> -- 
> You received this message because you are subscribed to a topic in the Google 
> Groups "sqlalchemy" group.
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> https://groups.google.com/d/topic/sqlalchemy/bkm3-nB6d1o/unsubscribe.
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[sqlalchemy] error related to setting attribute to same value twice

[lars van gemerden]

Hi all,

I have a one-to-one and many-to-one relationship (with an association table 
in the middle; Report.author-assoctable-Person.reports; why the table in 
the middle, you might ask, well it's a long story) and i am setting the 
author on a specific Report twice to the same value. This gives the 
following error:

   InvalidRequestError: Can't attach instance ; another instance with key (, (2,)) is already present in this session.

The first time i set the author, it works and if i change the author it 
works as well.

This seems i little strange to me, why not be able to set the attribute to 
the same value twice?

Otherwise i have to check whether the new and old values are equal (which 
through the peculiarties of my code is somewhat wastefull) 

Cheers, Lars 

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Re: [sqlalchemy] alternate way to filter queries

[lars van gemerden]

Hmm, too bad. I do have the lambda methods in string form so i'll probably 
have to write a parser and construct the query with unions and intersects 
(or filter(A.b > 1, A.c<0) like calls instead of intersects).

No how did writing a parser tree go |-)?

CL

On Monday, August 26, 2013 8:27:16 PM UTC+2, Simon King wrote:
>
>
> On 26 Aug 2013, at 19:15, lars van gemerden 
> > 
> wrote: 
> > 
> > On Monday, August 26, 2013 5:23:07 PM UTC+2, Michael Bayer wrote: 
> > 
> > On Aug 26, 2013, at 11:14 AM, lars van gemerden  
> wrote: 
> > 
> >> Hi all, 
> >> 
> >> This might be a bit of a stretch but here it goes: 
> >> 
> >> Say that i have a lambda function that takes a mapped object and 
> teturns whether it is valid; e.g: 
> >> 
> >> lambda person: person.age > 17 or person.length > 1.75 
> >> 
> >> is it possible to use this method to perform an sqla query on the 
> database? Perhaps by using hybrid_method? 
> >> 
> >> Cheers, Lars 
> >> 
> >> PS: this might seem strange question, but it would save me a lot of 
> work and/or would make my internal and user interfaces a lot more 
> consistent. 
> >> 
> >> PPS: i do also have a string representation of the lambda functions, if 
> that helps 
> > 
> > 
> > I'm not sure if you need these to remain as lambdas, sure you can just 
> pass it to a hybrid_method: 
> > 
> > class MyClass(Base): 
> > #  
> > 
> >@hybrid_method 
> >def run_compare(self, fn, *args): 
> > return fn(*args) 
> > 
> > 
> > query(MyClass).filter(MyClass.run_compare(some_lambda, 
> some_other_object)) 
> > 
> >   
> > 
> > Hi Michael, 
> > 
> > So just to be sure, if i understand correctly and i have: 
> > 
> >func  = lambda person: person.age > 17 or person.length > 1.75 
> > 
> > I can do: 
> > 
> >class Person(Base): 
> >#  
> > 
> >   @hybrid_method 
> >   def run_filter(self, fn): 
> >return fn(self) 
> > 
> >   session.query(MyClass).filter(MyClass.run_compare(func)) 
> > 
> > to get all objects of class Person where obj.age>17 or obj.length>1.75   
> > 
> > Is that without loading all records and filtering afterwards?? 
> > 
> > That's pretty impressive i think (and really helpful to me personally) 
> > 
> > Cheers, Lars 
>
>
> As long as your function returns something meaningful when called with the 
> class (Person) rather than an instance, it should be fine. 
>
> Unfortunately I'm not sure your example will work, because " or 
> " isn't something that SQLAlchemy can convert into an SQL statement. 
> If you were able to use the bitwise "or" operator "|" instead, that would 
> do the right thing. See the "contains" and "intersects" methods in the 
> first example on 
> http://docs.sqlalchemy.org/en/rel_0_8/orm/extensions/hybrid.html. 
>
> Hope that helps, 
>
> Simon

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Re: [sqlalchemy] alternate way to filter queries

[lars van gemerden]

Hi Michael,

So just to be sure, if i understand correctly and i have:

   func  = lambda person: person.age > 17 or person.length > 1.75

I can do:

   class Person(Base):
   # 

  @hybrid_method
  def run_filter(self, fn):
   return fn(self)

  session.query(MyClass).filter(MyClass.run_compare(func))

to get all objects of class Person where obj.age>17 or obj.length>1.75  

Is that without loading all records and filtering afterwards??

That's pretty impressive i think (and really helpful to me personally)

Cheers, Lars



On Monday, August 26, 2013 5:23:07 PM UTC+2, Michael Bayer wrote:
>
>
> On Aug 26, 2013, at 11:14 AM, lars van gemerden 
> > 
> wrote:
>
> Hi all,
>
> This might be a bit of a stretch but here it goes:
>
> Say that i have a lambda function that takes a mapped object and teturns 
> whether it is valid; e.g:
>
> lambda person: person.age > 17 or person.length > 1.75
>
> is it possible to use this method to perform an sqla query on the 
> database? Perhaps by using hybrid_method?
>
> Cheers, Lars
>
> PS: this might seem strange question, but it would save me a lot of work 
> and/or would make my internal and user interfaces a lot more consistent. 
>
> PPS: i do also have a string representation of the lambda functions, if 
> that helps
>
>
>
> I'm not sure if you need these to remain as lambdas, sure you can just 
> pass it to a hybrid_method:
>
> class MyClass(Base):
> # 
>
>@hybrid_method
>def run_compare(self, fn, *args):
> return fn(*args)
>
>
> query(MyClass).filter(MyClass.run_compare(some_lambda, some_other_object))
>

 

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[sqlalchemy] alternate way to filter queries

[lars van gemerden]

Hi all,

This might be a bit of a stretch but here it goes:

Say that i have a lambda function that takes a mapped object and teturns 
whether it is valid; e.g:

lambda person: person.age > 17 or person.length > 1.75

is it possible to use this method to perform an sqla query on the database? 
Perhaps by using hybrid_method?

Cheers, Lars

PS: this might seem strange question, but it would save me a lot of work 
and/or would make my internal and user interfaces a lot more consistent. 

PPS: i do also have a string representation of the lambda functions, if 
that helps

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Re: [sqlalchemy] possible bug in InstrumentedAttribute.__delete__?

[lars van gemerden]

Now i was doing both, but you're right, i can remove the default from the 
column definition, and just initialise the object with the default in 
__init__ (from metadata i created elsewhere, but will remain available). 
Setting the default ASAP (on object creation) seems like the way of least 
surprise and it's not hard to do, as Wichert mentioned.

Thanks again, Michael, my code improves ...

Lars

On Saturday, July 13, 2013 10:59:08 PM UTC+2, Michael Bayer wrote:
>
>
> On Jul 13, 2013, at 3:21 PM, Lars van Gemerden 
> > 
> wrote: 
>
> > Just trying to help; i am not sure, but what you might also consider is 
> to initialise attributes (or on first access) with a default if a default 
> value as Column argument is given (i am already doing this in my own code) 
> and also reset to this default in case of del, but maybe there are 
> disadvantages. 
>
> I can see why that might be reasonable, but at the same time the "default" 
> for Column is at the level of Core; the "default" could be a Python 
> callable, and this callable could be relying upon the fact that it is 
> invoked within the context of executing the INSERT statement.By pulling 
> out the Core-level "default" upon attribute access and just populating at 
> the ORM level means we bypass the Core in doing its normal job with 
> "default", which violates . there's a term for this I can't recall, but 
> the idea is, "A does job X using mechanism P" therefore if, based on some 
> very non-deterministic system, once in awhile "B does job X using mechanism 
> Q" instead, it makes the code much harder to understand and debug.  So 
> to really do it this way, the contract of "default" in terms of the ORM 
> would need to be modified completely, such that *all* Column "default" args 
> are applied at the ORM level.   But even then, your Column() is still 
> behaving in two different ways based on if you use Session.add() or 
> engine.execute(insert()). 
>
> The original intent of "default" for Column is that it acts exactly like 
> "server_default", except it runs on the Python side for the case that your 
> schema wasn't created with this default, or the functionality of your 
> default is not supported by the database.  But otherwise, just like a 
> "server_default", the value is None on the Python side until the INSERT 
> occurs. 
>
> Really, a better solution here would be an ORM-level "default", that's 
> what you've implemented anyway.   
>
>
>

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Re: [sqlalchemy] possible bug in InstrumentedAttribute.__delete__?

[Lars van Gemerden]

Just trying to help; i am not sure, but what you might also consider is to 
initialise attributes (or on first access) with a default if a default value as 
Column argument is given (i am already doing this in my own code) and also 
reset to this default in case of del, but maybe there are disadvantages.

Cheers, Lars




Lars van Gemerden
l...@rational-it.com
+31 6 26 88 55 39


On 13 jul. 2013, at 20:02, Michael Bayer  wrote:

> 
> On Jul 13, 2013, at 10:24 AM, Lars van Gemerden  wrote:
> 
>> I think i didn't explain the error enough; just calling del user.name in the 
>> example below causes an exception (except when i already accessed (say print 
>> user.name) the attribute, which seemed odd to me). This is independent of 
>> whether the attr becomes None. 
>> 
>> Otherwise it isn't a real problem in my code, just something i ran into 
>> while cleaning up some internal api, as you say i can easily work around it.
> 
> Great then, yes we don't do a good job with "del" but there is a logic to it 
> which I can't be 100% sure some apps aren't relying upon.I can possibly 
> make it behave intuitively for 0.9, I guess it should mean, "set the 
> attribute to None" - this because as you might have noticed an instrumented 
> column attribute defaults itself to "None" when first accessed.
> 
> -- 
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Re: [sqlalchemy] possible bug in InstrumentedAttribute.__delete__?

[Lars van Gemerden]

I think i didn't explain the error enough; just calling del user.name in the 
example below causes an exception (except when i already accessed (say print 
user.name) the attribute, which seemed odd to me). This is independent of 
whether the attr becomes None. 

Otherwise it isn't a real problem in my code, just something i ran into while 
cleaning up some internal api, as you say i can easily work around it.

Cheers, Lars



========
Lars van Gemerden
l...@rational-it.com
+31 6 26 88 55 39


On 13 jul. 2013, at 01:52, Michael Bayer  wrote:

> There's all kinds of things that __delete__ should possibly do, most likely 
> just do what you expect, i.e. set the value to NULL, but this would be 
> changing its behavior in a very backwards-incompatible way; such a change 
> could only be considered for 0.9.
> 
> Whats not clear is how exactly an entire application was built around 0.7, 
> relying on "del" in some way such that this can no longer be changed, and 
> suddenly it's an issue?  doesn't make sense, I don't see why you can't just 
> get replace those "del" statements on your end.  It's not supported, and if 
> it were, it would not be in 0.7 or 0.8.
> 
> 
> 
> On Jul 12, 2013, at 6:11 PM, Lars van Gemerden  wrote:
> 
>> After thinking on it some more, should InstrumentedAttribute.__delete__ even 
>> exist then, or maybe raise a NotImplementedError?
>> 
>> CL
>> 
>> 
>> Lars van Gemerden
>> l...@rational-it.com
>> +31 6 26 88 55 39
>> 
>> 
>> On 12 jul. 2013, at 18:28, Michael Bayer  wrote:
>> 
>>> We've never supported "del obj.attrname" as a means of setting an attribute 
>>> to None (which translates to NULL in SQL).   Setting the value to None 
>>> explicitly is preferred.
>>> 
>>> On Jul 12, 2013, at 12:16 PM, lars van gemerden  
>>> wrote:
>>> 
>>>> Hi all,
>>>> 
>>>> I had an arror in my code and i think i have reconstructed it as follows:
>>>> 
>>>> ---
>>>> 
>>>> from sqlalchemy import Column, Integer, String
>>>> from sqlalchemy import create_engine
>>>> from sqlalchemy.orm import sessionmaker
>>>> from sqlalchemy.ext.declarative import declarative_base
>>>> 
>>>> Base = declarative_base()
>>>> engine = create_engine('sqlite:///:memory:', echo=True)
>>>> Session = sessionmaker(bind=engine)
>>>> 
>>>> class User(Base):
>>>> __tablename__ = 'users'
>>>> id = Column(Integer, primary_key=True)
>>>> name = Column(String)
>>>> 
>>>> Base.metadata.create_all(engine) 
>>>> 
>>>> session = Session()
>>>> user = User(name = 'bob')
>>>> session.add(user)
>>>> session.commit()
>>>> #user.name
>>>> del user.name #error in sqlalchemy file attributes.py line 529
>>>> #user.name
>>>> session.commit()
>>>> assert user.name == None #error: user.name is still 'bob'
>>>> 
>>>> 
>>>> 
>>>> These two errors do not occur if i access the attributes before the delete 
>>>> or the commit (i.e. uncomment the #user.name lines).
>>>> 
>>>> I am using version 7.5; are these errors solved by the latest version?
>>>> 
>>>>  I would like to avoid upgrading at this point, but if i could be 
>>>> reasonably sure that upgrading solves the problem, then no problem ..
>>>> 
>>>> Cheers, Lars
>>>> 
>>>> 
>>>> 
>>>> -- 
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>>>> email to sqlalchemy+unsubscr...@googlegroups.com.
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Re: [sqlalchemy] possible bug in InstrumentedAttribute.__delete__?

[Lars van Gemerden]

After thinking on it some more, should InstrumentedAttribute.__delete__ even 
exist then, or maybe raise a NotImplementedError?

CL


Lars van Gemerden
l...@rational-it.com
+31 6 26 88 55 39


On 12 jul. 2013, at 18:28, Michael Bayer  wrote:

> We've never supported "del obj.attrname" as a means of setting an attribute 
> to None (which translates to NULL in SQL).   Setting the value to None 
> explicitly is preferred.
> 
> On Jul 12, 2013, at 12:16 PM, lars van gemerden  wrote:
> 
>> Hi all,
>> 
>> I had an arror in my code and i think i have reconstructed it as follows:
>> 
>> ---
>> 
>> from sqlalchemy import Column, Integer, String
>> from sqlalchemy import create_engine
>> from sqlalchemy.orm import sessionmaker
>> from sqlalchemy.ext.declarative import declarative_base
>> 
>> Base = declarative_base()
>> engine = create_engine('sqlite:///:memory:', echo=True)
>> Session = sessionmaker(bind=engine)
>> 
>> class User(Base):
>> __tablename__ = 'users'
>> id = Column(Integer, primary_key=True)
>> name = Column(String)
>> 
>> Base.metadata.create_all(engine) 
>> 
>> session = Session()
>> user = User(name = 'bob')
>> session.add(user)
>> session.commit()
>> #user.name
>> del user.name #error in sqlalchemy file attributes.py line 529
>> #user.name
>> session.commit()
>> assert user.name == None #error: user.name is still 'bob'
>> 
>> 
>> 
>> These two errors do not occur if i access the attributes before the delete 
>> or the commit (i.e. uncomment the #user.name lines).
>> 
>> I am using version 7.5; are these errors solved by the latest version?
>> 
>>  I would like to avoid upgrading at this point, but if i could be reasonably 
>> sure that upgrading solves the problem, then no problem ..
>> 
>> Cheers, Lars
>> 
>> 
>> 
>> -- 
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Re: [sqlalchemy] possible bug in InstrumentedAttribute.__delete__?

[Lars van Gemerden]

Can i just override __delattr__ in a subclass of a declarative base to achieve 
this anyway?

Cheers, Lars


Lars van Gemerden
l...@rational-it.com
+31 6 26 88 55 39


On 12 jul. 2013, at 18:28, Michael Bayer  wrote:

> We've never supported "del obj.attrname" as a means of setting an attribute 
> to None (which translates to NULL in SQL).   Setting the value to None 
> explicitly is preferred.
> 
> On Jul 12, 2013, at 12:16 PM, lars van gemerden  wrote:
> 
>> Hi all,
>> 
>> I had an arror in my code and i think i have reconstructed it as follows:
>> 
>> ---
>> 
>> from sqlalchemy import Column, Integer, String
>> from sqlalchemy import create_engine
>> from sqlalchemy.orm import sessionmaker
>> from sqlalchemy.ext.declarative import declarative_base
>> 
>> Base = declarative_base()
>> engine = create_engine('sqlite:///:memory:', echo=True)
>> Session = sessionmaker(bind=engine)
>> 
>> class User(Base):
>> __tablename__ = 'users'
>> id = Column(Integer, primary_key=True)
>> name = Column(String)
>> 
>> Base.metadata.create_all(engine) 
>> 
>> session = Session()
>> user = User(name = 'bob')
>> session.add(user)
>> session.commit()
>> #user.name
>> del user.name #error in sqlalchemy file attributes.py line 529
>> #user.name
>> session.commit()
>> assert user.name == None #error: user.name is still 'bob'
>> 
>> 
>> 
>> These two errors do not occur if i access the attributes before the delete 
>> or the commit (i.e. uncomment the #user.name lines).
>> 
>> I am using version 7.5; are these errors solved by the latest version?
>> 
>>  I would like to avoid upgrading at this point, but if i could be reasonably 
>> sure that upgrading solves the problem, then no problem ..
>> 
>> Cheers, Lars
>> 
>> 
>> 
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[sqlalchemy] possible bug in InstrumentedAttribute.__delete__?

[lars van gemerden]

Hi all,

I had an arror in my code and i think i have reconstructed it as follows:

---

from sqlalchemy import Column, Integer, String
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()
engine = create_engine('sqlite:///:memory:', echo=True)
Session = sessionmaker(bind=engine)

class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String)

Base.metadata.create_all(engine) 

session = Session()
user = User(name = 'bob')
session.add(user)
session.commit()
#user.name
del user.name #error in sqlalchemy file attributes.py line 529
#user.name
session.commit()
assert user.name == None #error: user.name is still 'bob'



These two errors do not occur if i access the attributes before the delete 
or the commit (i.e. uncomment the #user.name lines).

I am using version 7.5; are these errors solved by the latest version?

 I would like to avoid upgrading at this point, but if i could be 
reasonably sure that upgrading solves the problem, then no problem ..

Cheers, Lars


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Re: [sqlalchemy] finding table/column name of unique constraint failure

[lars van Gemerden]

Thanks, Michael


On Mon, May 20, 2013 at 12:52 AM, Michael Bayer wrote:

>
> On May 19, 2013, at 4:39 AM, lars van gemerden 
> wrote:
>
> > Hi all,
> >
> > I generate webpages in which end-users can input data that is stored in
> a database via sqla.The datamodel is not pre-defined but created by (other)
> users/designers.
> >
> > My question is how can i best let the end-user know which field contains
> the error if the end-user violates a unique constraint; e.g. if the user
> creates an account by filling in a username/password, the username must be
> unique so the user must get an error ("username already exists" oss) if he
> tries to fill in an existing username.
> >
> > If i commit the data, the exception thrown is somewhat cryptic (is the
> message created by sqla or the database?).
> >
> > Some related questions:
> >
> > - are there arguments in the exception i could use?
> > - should i just query the table for the existence of the unique
> constrained value (i seem to remember that is impossible in the "validate"
> solution, so how else)?
> >
> > I might be able to come up with some sort of solution, but i am looking
> for a good/the best (structurally sound, not too slow, not overly complex)
> solution, also useable for other constraints (e.g. non-null, maybe other
> query/multi-record based constraints).
>
> the messages are generated by the database and the DBAPI in use,
> SQLAlchemy just passes them through.  There's no standardization for those
> messages, so if your target database isn't providing enough parseable
> information, you may need to do a quick query against the unique fields on
> the table first in order to produce validation logic.
>
>
> --
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-- 

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l...@rational-it.com
+31 6 26 88 55 39


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[sqlalchemy] finding table/column name of unique constraint failure

[lars van gemerden]

Hi all,

I generate webpages in which end-users can input data that is stored in a 
database via sqla.The datamodel is not pre-defined but created by (other) 
users/designers.   

My question is how can i best let the end-user know which field contains 
the error if the end-user violates a unique constraint; e.g. if the user 
creates an account by filling in a username/password, the username must be 
unique so the user must get an error ("username already exists" oss) if he 
tries to fill in an existing username.

If i commit the data, the exception thrown is somewhat cryptic (is the 
message created by sqla or the database?). 

Some related questions:

- are there arguments in the exception i could use?
- should i just query the table for the existence of the unique constrained 
value (i seem to remember that is impossible in the "validate" solution, so 
how else)?

I might be able to come up with some sort of solution, but i am looking for 
a good/the best (structurally sound, not too slow, not overly complex) 
solution, also useable for other constraints (e.g. non-null, maybe other 
query/multi-record based constraints). 

Cheers, Lars

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[sqlalchemy] Re: adding validates() decorator after class creation

[lars van gemerden]

Perfect (almost ;-), thanks a lot!

for future reference, the attribute name (key) was needed 
in create_validator(cls) to access the correct validate method:

@staticmethod
def _create_validator(key, cls): 
def validate(target, value, oldvalue, initiator):
if not cls._type_[key].validate(value):
raise ValueError("incorrect value '%s' for '%s' in '%s'" % 
(str(value), key, cls.__name__))
return validate

def create_validators(self):  
for cls in self.itervalues():
for fld in cls._type_.fields():
key = fld.key()
attribute = getattr(cls, key)
event.listen(attribute, "set", self._create_validator(key, 
cls))
debug_print('created validator for %s in %s' % (key, 
cls.__name__))

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[sqlalchemy] adding validates() decorator after class creation

[lars van gemerden]

Hi,

I am trying to use validates() to dynamically add validation to my sqla 
classes, but i cannot figure out how to do this. I have read python 
decorator docs and docs n validates, but something escapes me (or it is 
just not possible).

A code snippet (this does not work):

def create_validators(self):  
for cls in self.itervalues():
names = tuple([fld.key() for fld in cls._type_.fields()])
def validator(obj, name, value):
if not cls._type_[name].validate(value):
raise ValueError("incorrect value '%s' for '%s' in 
'%s'" % (str(value), name, cls.__name__))
return value
setattr(cls, 'validator', validates(*names)(validator)) #does 
NOT work

in which:

'self' is a dictionary of sqla classes, 
'cls' is an sqla class (derived from declarative_base(...)), 
'cls._type_' contains the information for (further) generation of 'cls' 
(e.g. cls._type_[name].validate(value) calls a validate method for value 
for a field (say String(50)) with name 'name')

The method above runs without problem, but the validator function is never 
called when setting field values. I have tried all alternatives i can think 
of, but maybe i am missing something basic.

Can anyone help?

Cheers, Lars




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[sqlalchemy] Re: automating inheritance

[lars van gemerden]

Well thats the thing, my users will determine the data structure
(graphically) and it is hard to predict what they will come up with.
On the other hand, I am only building a prototype at the moment, so
speed issues (if not easily solved) will have to wait.

I'll stick with joined inheritance for now (though I'll probalby take
out the unique base class for all classes).

Thank you again for all the help,

Lars

On Apr 27, 3:59 pm, Michael Bayer  wrote:
> concrete inheritance is very challenging overall, if you expect there to be 
> any kind of polymorphic interaction between the classes.     if you want to 
> query polymorphically then speed will be probably worse.   If you can do 
> without polymorphic and stick to each subclass directly it wont have an issue.
>
> Usually though if I'm inheriting more than two levels, I'll use joined 
> inheritance for level one->two then single table for all levels beyond that.  
>  Depends on what you're trying to do.
>
> On Apr 27, 2012, at 3:05 AM, lars van gemerden wrote:
>
>
>
>
>
>
>
> > Ok, so speed might become an issue for me as well;
>
> > Do you think a similar metaclass approach would work for concrete 
> > inheritance would work without major drawbacks (before i do a major 
> > overhaul)?
> > Is there any indication about how much faster concrete inheritance is, 
> > compared to joined inheritance?
>
> > Cheers, Lars
>
> > On Friday, April 20, 2012 9:32:49 PM UTC+2, Michael Bayer wrote:
>
> > On Apr 20, 2012, at 8:51 AM, lars van gemerden wrote:
> > > Ok, thank you, that helps, but now i cannot inherit from Engineer, as in:
>
> > > class BaseMixin(object):
>
> > >     discriminator = Column(String(50))
>
> > >     @declared_attr
> > >     def __tablename__(cls):
> > >         return cls.__name__
> > >     @declared_attr
> > >     def id(cls):
> > >         return Column(Integer, primary_key = True)
> > >     @declared_attr
> > >     def __mapper_args__(cls):
> > >         if not has_inherited_table(cls):
> > >             return {'polymorphic_on': 'discriminator'}
> > >         else:
> > >             return {'polymorphic_identity': cls.__name__}
>
> > > class InheritMixin(BaseMixin):
> > >     @declared_attr
> > >     def id(cls):
> > >         super_id = super(InheritMixin, cls).id
> > >         return Column(Integer, ForeignKey(super_id), primary_key = True)
>
> > > class Person(BaseMixin, Base):
> > >     name = Column(String(50))
>
> > > class Engineer(InheritMixin, Person):
> > >     job = Column(String(50))
>
> > > class MasterEngineer(InheritMixin, Engineer):
> > >     specialty = Column(String(50))
>
> > > Gives an MRO() error and if i would reverse the baseclasses (like class 
> > > Engineer(Person, InheritMixin):  ... ), the inheriting classes pick up 
> > > the wrong id.
>
> > > Do you see any solution for this?
>
> > yeah I suppose if you're building out joined inheritance more than one 
> > level then this becomes awkward.   I never use joined inh more than one 
> > level because it has too much of an impact on queries.
>
> > the metaclass as you mention is always the last resort when the various 
> > declarative trickery reaches its limit.   I'm not thrilled about the 
> > metaclass approach because it quickly gets confusing and shouldn't be 
> > necessary.   though in this case without some extra mechanism on 
> > declarative, such as a __pre_declare__() method of some kind, it might be 
> > the only approach.
>
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Re: [sqlalchemy] Re: automating inheritance

[lars van gemerden]

Ok, so speed might become an issue for me as well; 

Do you think a similar metaclass approach would work for concrete 
inheritance would work without major drawbacks (before i do a major 
overhaul)?
Is there any indication about how much faster concrete inheritance is, 
compared to joined inheritance?

Cheers, Lars

On Friday, April 20, 2012 9:32:49 PM UTC+2, Michael Bayer wrote:
>
>
> On Apr 20, 2012, at 8:51 AM, lars van gemerden wrote:
>
> > Ok, thank you, that helps, but now i cannot inherit from Engineer, as in:
> > 
> > class BaseMixin(object):
> > 
> > discriminator = Column(String(50))
> > 
> > @declared_attr
> > def __tablename__(cls):
> > return cls.__name__
> > @declared_attr
> > def id(cls):
> > return Column(Integer, primary_key = True)
> > @declared_attr
> > def __mapper_args__(cls):
> > if not has_inherited_table(cls):
> > return {'polymorphic_on': 'discriminator'}
> > else:
> > return {'polymorphic_identity': cls.__name__}
> > 
> > 
> > class InheritMixin(BaseMixin):
> > @declared_attr
> > def id(cls):
> > super_id = super(InheritMixin, cls).id
> > return Column(Integer, ForeignKey(super_id), primary_key = True)
> > 
> > class Person(BaseMixin, Base):
> > name = Column(String(50))
> >
> > class Engineer(InheritMixin, Person):
> > job = Column(String(50))
> > 
> > class MasterEngineer(InheritMixin, Engineer):
> > specialty = Column(String(50))
> > 
> > Gives an MRO() error and if i would reverse the baseclasses (like class 
> Engineer(Person, InheritMixin):  ... ), the inheriting classes pick up the 
> wrong id.
> > 
> > Do you see any solution for this? 
>
> yeah I suppose if you're building out joined inheritance more than one 
> level then this becomes awkward.   I never use joined inh more than one 
> level because it has too much of an impact on queries.
>
> the metaclass as you mention is always the last resort when the various 
> declarative trickery reaches its limit.   I'm not thrilled about the 
> metaclass approach because it quickly gets confusing and shouldn't be 
> necessary.   though in this case without some extra mechanism on 
> declarative, such as a __pre_declare__() method of some kind, it might be 
> the only approach.
>
>

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Re: [sqlalchemy] Re: automating inheritance

[lars van gemerden]

Hi Mike,

How about this approach with a custom metaclass; so far it works and seems 
the cleanest to me:

from sqlalchemy import *
from sqlalchemy.orm.session import sessionmaker
from sqlalchemy.ext.declarative import declarative_base, 
has_inherited_table, DeclarativeMeta

engine = create_engine('sqlite:///:memory:', echo=False)

class InheritMeta(DeclarativeMeta):

def __init__(cls, name, bases, clsdict):
cls.__tablename__ = cls.__name__
if not has_inherited_table(cls):
cls.id = Column(Integer, primary_key = True)
cls.discriminator = Column(String(50))
cls.__mapper_args__ = {'polymorphic_on': 'discriminator'}
else:
cls.id = Column(Integer, ForeignKey(bases[0].id), primary_key = 
True)
cls.__mapper_args__ = {'polymorphic_identity': cls.__name__}
super(InheritMeta, cls).__init__(name, bases, clsdict)

InheritableBase = declarative_base(bind = engine, metaclass = InheritMeta)

class Person(InheritableBase):
name = Column(String(50))
   
class Engineer(Person):
job = Column(String(50))

class MasterEngineer(Engineer):
specialty = Column(String(50))


if __name__ == '__main__':
InheritableBase.metadata.create_all(engine)
session = sessionmaker(bind=engine)()

a = Person(name = 'ann')
b = Engineer(name = 'bob', job = 'car repair')
c = MasterEngineer(name = 'carl', job = 'car repair', specialty = 
'tires')
session.add_all([a, b, c])
session.commit()
people = session.query(Person).all()
print people

Do you see any drawbacks, gotchas for later on?

Regards, Lars

On Friday, April 20, 2012 12:41:28 PM UTC+2, Michael Bayer wrote:
>
>
> On Apr 20, 2012, at 4:59 AM, lars van gemerden wrote:
>
> > this is the testcase:
> > 
> > 
> > What am i missing?
>
>
> the issue here is one of Python inheritance mechanics.   Declarative calls 
> upon @declared_attr in terms of the class, that is, we look through the 
> class to find each @declared_attr, but when we find one, we invoke it by 
> just calling it as a method, that is, getattr(cls, name).   This works for 
> things like __mapper_args__ which remain as callable methods on classes 
> like Person, Engineer.   But "id", when that is declared on Person is 
> immediately replaced with a mapping.   By the time you get to Engineer, the 
> id() method is gone.
>
> So for inheriting cases you need to build a mixin that is applied to every 
> subclass.  This makes sense because a mixin with a column on it implies 
> that the column is being associated only with that immediate class - if you 
> wanted a subclass to act as single table inheritance, you'd omit this 
> class.  In this case you want the same column on all subclasses.So you 
> can do it like this (note also using declarative.has_inherited_table 
> helper):
>
> class InheritMixin(object):
>
>@declared_attr
>def __tablename__(cls):
>return cls.__name__
>
>@declared_attr
>def id(cls):
>return Column(Integer, primary_key = True)
>
>@declared_attr
>def __mapper_args__(cls):
>if not has_inherited_table(cls):
>return {'polymorphic_on': 'discriminator'}
>else:
>return {'polymorphic_identity': cls.__name__}
>
> class Inherits(InheritMixin):
> @declared_attr
> def id(cls):
> super_id = super(Inherits, cls).id
> return Column(Integer, ForeignKey(super_id),primary_key = True)
>
> class Person(InheritMixin, Base):
>discriminator = Column(String(50))
>name = Column(String(50))
>
> class Engineer(Inherits, Person):
>job = Column(String(50))
>
>
> this should be in the docs so I've added ticket #2471 to handle this.
>
> > 
> > Cheers, Lars
> > 
> > 
> > On Apr 19, 4:13 pm, Michael Bayer  wrote:
> >> On Apr 19, 2012, at 6:23 AM, lars van gemerden wrote:
> >> 
> >> 
> >> 
> >> 
> >> 
> >> 
> >> 
> >> 
> >> 
> >>> I am trying to my my joined inheritance code clearer, for the dynamic
> >>> generation of sa classes and tried to do something like this:
> >> 
> >>> class InheritMixin(object):
> >> 
> >>>@declared_attr
> >>>def __tablename__(cls):
> >>>return cls.__name__
> >>>@declared_attr
> >>>def id(cls):
> >>>if cls.__name__ == 'Object':
> >>>return Column(Integer, primary_key = True)
> >>>

Re: [sqlalchemy] Re: automating inheritance

[lars van gemerden]

Ok, thank you, that helps, but now i cannot inherit from Engineer, as in:

class BaseMixin(object):

discriminator = Column(String(50))

@declared_attr
def __tablename__(cls):
return cls.__name__
@declared_attr
def id(cls):
return Column(Integer, primary_key = True)
@declared_attr
def __mapper_args__(cls):
if not has_inherited_table(cls):
return {'polymorphic_on': 'discriminator'}
else:
return {'polymorphic_identity': cls.__name__}


class InheritMixin(BaseMixin):
@declared_attr
def id(cls):
super_id = super(InheritMixin, cls).id
return Column(Integer, ForeignKey(super_id), primary_key = True)

class Person(BaseMixin, Base):
name = Column(String(50))
   
class Engineer(InheritMixin, Person):
job = Column(String(50))

class MasterEngineer(InheritMixin, Engineer):
specialty = Column(String(50))

Gives an MRO() error and if i would reverse the baseclasses (like class 
Engineer(Person, InheritMixin):  ... ), the inheriting classes pick up the 
wrong id.

Do you see any solution for this? 

BTW: could i just move

@declared_attr
def __mapper_args__(cls):
return {'polymorphic_identity': cls.__name__}

to InheritMixin instead of doing the 'has_inherited_table' if-statement in 
BaseMixin?

Cheers, Lars


On Friday, April 20, 2012 12:41:28 PM UTC+2, Michael Bayer wrote:
>
>
> On Apr 20, 2012, at 4:59 AM, lars van gemerden wrote:
>
> > this is the testcase:
> > 
> > 
> > What am i missing?
>
>
> the issue here is one of Python inheritance mechanics.   Declarative calls 
> upon @declared_attr in terms of the class, that is, we look through the 
> class to find each @declared_attr, but when we find one, we invoke it by 
> just calling it as a method, that is, getattr(cls, name).   This works for 
> things like __mapper_args__ which remain as callable methods on classes 
> like Person, Engineer.   But "id", when that is declared on Person is 
> immediately replaced with a mapping.   By the time you get to Engineer, the 
> id() method is gone.
>
> So for inheriting cases you need to build a mixin that is applied to every 
> subclass.  This makes sense because a mixin with a column on it implies 
> that the column is being associated only with that immediate class - if you 
> wanted a subclass to act as single table inheritance, you'd omit this 
> class.  In this case you want the same column on all subclasses.So you 
> can do it like this (note also using declarative.has_inherited_table 
> helper):
>
> class InheritMixin(object):
>
>@declared_attr
>def __tablename__(cls):
>return cls.__name__
>
>@declared_attr
>def id(cls):
>return Column(Integer, primary_key = True)
>
>@declared_attr
>def __mapper_args__(cls):
>if not has_inherited_table(cls):
>return {'polymorphic_on': 'discriminator'}
>else:
>return {'polymorphic_identity': cls.__name__}
>
> class Inherits(InheritMixin):
> @declared_attr
> def id(cls):
> super_id = super(Inherits, cls).id
> return Column(Integer, ForeignKey(super_id),primary_key = True)
>
> class Person(InheritMixin, Base):
>discriminator = Column(String(50))
>name = Column(String(50))
>
> class Engineer(Inherits, Person):
>job = Column(String(50))
>
>
> this should be in the docs so I've added ticket #2471 to handle this.
>
> > 
> > Cheers, Lars
> > 
> > 
> > On Apr 19, 4:13 pm, Michael Bayer  wrote:
> >> On Apr 19, 2012, at 6:23 AM, lars van gemerden wrote:
> >> 
> >> 
> >> 
> >> 
> >> 
> >> 
> >> 
> >> 
> >> 
> >>> I am trying to my my joined inheritance code clearer, for the dynamic
> >>> generation of sa classes and tried to do something like this:
> >> 
> >>> class InheritMixin(object):
> >> 
> >>>@declared_attr
> >>>def __tablename__(cls):
> >>>return cls.__name__
> >>>@declared_attr
> >>>def id(cls):
> >>>if cls.__name__ == 'Object':
> >>>return Column(Integer, primary_key = True)
> >>>else:
> >>>print 'in id: ', cls.__name__, cls.__bases__[0].__name__
> >>>return Column(Integer,
> >>> ForeignKey(cls.__bases__[0].__name__ + '.id'), primary_key = True)
> >>>@declared_attr
> >>>def __mapper_args__(cls):
&g

[sqlalchemy] Re: automating inheritance

[lars van gemerden]

this is the testcase:

from sqlalchemy import *
from sqlalchemy.orm.session import sessionmaker
from sqlalchemy.ext.declarative import declarative_base, declared_attr

engine = create_engine('sqlite:///:memory:', echo=False)
Base = declarative_base(bind = engine)
Session = sessionmaker(bind = engine)

def setup(engine):
Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine)
return Session()

class InheritMixin(object):

@declared_attr
def __tablename__(cls):
return cls.__name__
@declared_attr
def id(cls):
if Base in cls.__bases__:
print 'base in id(cls): ', cls
return Column(Integer, primary_key = True)
else:
print 'in id(cls): ', cls, cls.__bases__[0]
return Column(Integer, ForeignKey(cls.__bases__[0].id),
primary_key = True)
@declared_attr
def __mapper_args__(cls):
if Base in cls.__bases__:
print 'base in __mapper_args__(cls): ', cls
return {'polymorphic_on': 'discriminator'}
else:
print 'in __mapper_args__(cls): ', cls, cls.__bases__[0],
cls.id, (cls.id is cls.__bases__[0].id)
return {'polymorphic_identity': cls.__name__}

class Person(Base, InheritMixin):
discriminator = Column(String(50))
name = Column(String(50))

class Engineer(Person):
job = Column(String(50))

if __name__ == '__main__':

session = setup(engine)
a = Person(name = 'ann')
b = Engineer(name = 'bob', job = 'car repair')
session.add_all([a, b])
session.commit()
people = session.query(Person).all()
print people

Note that i left out the 'inherit_condition', because without there is
already a problem:

base in id(cls):  
base in mapper_args(cls):  
in mapper_args(cls):Person.id True
Traceback (most recent call last):
  File "D:\Documents\Code\Eclipse\workspace\process_data3\src
\little_tests2.py", line 40, in 
class Engineer(Person):
  File "C:\Python27\lib\site-packages\sqlalchemy\ext\declarative.py",
line 1336, in __init__
_as_declarative(cls, classname, cls.__dict__)
  File "C:\Python27\lib\site-packages\sqlalchemy\ext\declarative.py",
line 1329, in _as_declarative
**mapper_args)
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\__init__.py",
line 1116, in mapper
return Mapper(class_, local_table, *args, **params)
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line
197, in __init__
self._configure_inheritance()
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line
473, in _configure_inheritance
self.local_table)
  File "C:\Python27\lib\site-packages\sqlalchemy\sql\util.py", line
303, in join_condition
"between '%s' and '%s'.%s" % (a.description, b.description, hint))
sqlalchemy.exc.ArgumentError: Can't find any foreign key relationships
between 'Person' and 'Engineer'.

What am i missing?

Cheers, Lars


On Apr 19, 4:13 pm, Michael Bayer  wrote:
> On Apr 19, 2012, at 6:23 AM, lars van gemerden wrote:
>
>
>
>
>
>
>
>
>
> > I am trying to my my joined inheritance code clearer, for the dynamic
> > generation of sa classes and tried to do something like this:
>
> > class InheritMixin(object):
>
> >    @declared_attr
> >    def __tablename__(cls):
> >        return cls.__name__
> >    @declared_attr
> >    def id(cls):
> >        if cls.__name__ == 'Object':
> >            return Column(Integer, primary_key = True)
> >        else:
> >            print 'in id: ', cls.__name__, cls.__bases__[0].__name__
> >            return Column(Integer,
> > ForeignKey(cls.__bases__[0].__name__ + '.id'), primary_key = True)
> >    @declared_attr
> >    def __mapper_args__(cls):
> >        if cls.__name__ == 'Object':
> >            return {'polymorphic_on': 'discriminator'}
> >        else:
> >            print 'in mapper_args: ', cls.__name__,
> > cls.__bases__[0].__name__
> >            return {'polymorphic_identity': cls.__name__,
> >                    'inherit_condition': (cls.id ==
> > cls.__bases__[0].id)}
>
> > Object = type('Object', (Base, InheritMixin), clsdict)
>
> > Where Object should be the (not necessarily direct) baseclass of all
> > inheriting classes. However I get errors: "Mapper Mapper|person|person
> > could not assemble any primary key columns for mapped table 'Join
> > object on Object(65389120) and person(65428224)' " etc ..
>
> im not sure of the ca

[sqlalchemy] automating inheritance

[lars van gemerden]

I am trying to my my joined inheritance code clearer, for the dynamic
generation of sa classes and tried to do something like this:


class InheritMixin(object):

@declared_attr
def __tablename__(cls):
return cls.__name__
@declared_attr
def id(cls):
if cls.__name__ == 'Object':
return Column(Integer, primary_key = True)
else:
print 'in id: ', cls.__name__, cls.__bases__[0].__name__
return Column(Integer,
ForeignKey(cls.__bases__[0].__name__ + '.id'), primary_key = True)
@declared_attr
def __mapper_args__(cls):
if cls.__name__ == 'Object':
return {'polymorphic_on': 'discriminator'}
else:
print 'in mapper_args: ', cls.__name__,
cls.__bases__[0].__name__
return {'polymorphic_identity': cls.__name__,
'inherit_condition': (cls.id ==
cls.__bases__[0].id)}

Object = type('Object', (Base, InheritMixin), clsdict)

Where Object should be the (not necessarily direct) baseclass of all
inheriting classes. However I get errors: "Mapper Mapper|person|person
could not assemble any primary key columns for mapped table 'Join
object on Object(65389120) and person(65428224)' " etc ..

I noticed that the method __mapper_args__(cls) is always called before
id(cls) (which is never called, probably due to the error.

Is there some way to fix this, while keeping the inheritance code in a
mixin?

Also, is there a way to add the discriminator column to the mixin (if
i just directly add it to the declaration, this gave another maybe
related error)?

Cheers, Lars

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[sqlalchemy] Re: dynamically adding a validates method

[lars van gemerden]

PS: the validate(value) method in typedef[name] is a normal method,
throwing exception on errors and returning the value when OK.

On Apr 16, 2:01 pm, lars van gemerden  wrote:
> Thank you, i got it working now. For future reference:
>
> Before creating a sa class with something like:
>
>     type(typename, (Base,), classdict)
>
> I first create the classdict in which I define columns, __tablename__,
> etc, and validators (relationships I add later).
>
> The validators i create(using a subclass of dict as classdict in the
> type() call, and typedef being an object holding the definition to be
> used to create a sa class/table) with:
>
>     def createValidator(self, typedef):
>             # get names of attributes to be validated:
>             names = [attr.name for attr in typedef.attributes \
>                        if attr.validates()]
>             #create validator method from validating method in the
> attr
>             #definition in typedef:
>             def validator(obj, name, value):
>                 return typedef[name].validate(value)
>             #turn into sa "@validate" descriptor (i don't get the
>             #mechanics completely, but still):
>             validates(*names)(validator)
>             #add to classdict
>             self['validator'] = validator
>
> Hope this helps someone, open to questions ...
>
> Cheers, Lars
>
> On Apr 15, 7:20 pm, Michael Bayer  wrote:
>
>
>
>
>
>
>
> > If you can't establish the event at class declaration time, then the 
> > @event.listens_for/event.listen() paradigm 
> > (seehttp://docs.sqlalchemy.org/en/latest/core/event.htmlforbackground) can 
> > be applied to the class-bound attribute (which here is "Positive.value") at 
> > any time.  "Positive.value" is an attribute generated by the mapping which 
> > is a result of using the declarative base.
>
> > On Apr 15, 2012, at 1:10 PM, lars van gemerden wrote:
>
> > > OK, this helps, so how do i do this if i do not know the name of the
> > > attribute to be checked  in advance(the "value" in
> > > @validates("value") )?
>
> > > On Apr 15, 6:52 pm, Michael Bayer  wrote:
> > >> using type() is equivalent to using a class declaration.   The end 
> > >> result is the same, as are the mechanics of what goes on both from a 
> > >> Python as well as a SQLAlchemy perspective.  So this works:
>
> > >> Positive = type("Positive", (Base,), dict(__tablename__ =
> > >> "positives",  value = Column(Integer)))
>
> > >> @event.listens_for(Positive.value, "set")
> > >> def checkvalue(target, value, oldvalue, initiator)
> > >>    assert value > 0
>
> > >> and also, since type() is equivalent to a class declaration, you can 
> > >> still use @validates,  if you pass the function into the class 
> > >> dictionary, so that it is part of the class before declarative sends it 
> > >> off to mapper():
>
> > >> @validates("value")
> > >> def checkvalue(self, name, value):
> > >>     assert value > 0
> > >>     return value
>
> > >> Positive = type("Positive", (Base,), dict(__tablename__ =
> > >> "positives",  value = Column(Integer), checkvalue=checkvalue))
>
> > >> On Apr 15, 2012, at 12:37 PM, lars van gemerden wrote:
>
> > >>> I don't know what "@validates hangs a marker of the method that
> > >>> mapper() uses when it instruments the class" means. I guess my
> > >>> question now becomes: How do I add the event.listens_for descriptor to
> > >>> the class, since i do not have a class declaration in the traditional
> > >>> sense?
>
> > >>> On Apr 15, 4:29 pm, Michael Bayer  wrote:
> > >>>> @validates hangs a marker of the method that mapper() uses when it 
> > >>>> instruments the class, so if the class is already mapped then that 
> > >>>> train has left the station.   Taking a cab instead, you can just add 
> > >>>> the attribute event directly:
>
> > >>>> @event.listens_for(Positive.value, "set")
> > >>>> def checkvalue(target, value, oldvalue, initiator)
> > >>>>    assert value > 0
>
> > >>>> if you want to return a new, mutated value then add retval=True to 
> > >>>> listens_for().
>
> > >>>> On Apr 15, 2012, at 8:22 AM, l

[sqlalchemy] Re: dynamically adding a validates method

[lars van gemerden]

Thank you, i got it working now. For future reference:

Before creating a sa class with something like:

type(typename, (Base,), classdict)

I first create the classdict in which I define columns, __tablename__,
etc, and validators (relationships I add later).

The validators i create(using a subclass of dict as classdict in the
type() call, and typedef being an object holding the definition to be
used to create a sa class/table) with:

def createValidator(self, typedef):
# get names of attributes to be validated:
names = [attr.name for attr in typedef.attributes \
   if attr.validates()]
#create validator method from validating method in the
attr
#definition in typedef:
def validator(obj, name, value):
return typedef[name].validate(value)
#turn into sa "@validate" descriptor (i don't get the
#mechanics completely, but still):
validates(*names)(validator)
#add to classdict
self['validator'] = validator

Hope this helps someone, open to questions ...

Cheers, Lars

On Apr 15, 7:20 pm, Michael Bayer  wrote:
> If you can't establish the event at class declaration time, then the 
> @event.listens_for/event.listen() paradigm 
> (seehttp://docs.sqlalchemy.org/en/latest/core/event.htmlfor background) can 
> be applied to the class-bound attribute (which here is "Positive.value") at 
> any time.  "Positive.value" is an attribute generated by the mapping which is 
> a result of using the declarative base.
>
> On Apr 15, 2012, at 1:10 PM, lars van gemerden wrote:
>
>
>
>
>
>
>
> > OK, this helps, so how do i do this if i do not know the name of the
> > attribute to be checked  in advance(the "value" in
> > @validates("value") )?
>
> > On Apr 15, 6:52 pm, Michael Bayer  wrote:
> >> using type() is equivalent to using a class declaration.   The end result 
> >> is the same, as are the mechanics of what goes on both from a Python as 
> >> well as a SQLAlchemy perspective.  So this works:
>
> >> Positive = type("Positive", (Base,), dict(__tablename__ =
> >> "positives",  value = Column(Integer)))
>
> >> @event.listens_for(Positive.value, "set")
> >> def checkvalue(target, value, oldvalue, initiator)
> >>    assert value > 0
>
> >> and also, since type() is equivalent to a class declaration, you can still 
> >> use @validates,  if you pass the function into the class dictionary, so 
> >> that it is part of the class before declarative sends it off to mapper():
>
> >> @validates("value")
> >> def checkvalue(self, name, value):
> >>     assert value > 0
> >>     return value
>
> >> Positive = type("Positive", (Base,), dict(__tablename__ =
> >> "positives",  value = Column(Integer), checkvalue=checkvalue))
>
> >> On Apr 15, 2012, at 12:37 PM, lars van gemerden wrote:
>
> >>> I don't know what "@validates hangs a marker of the method that
> >>> mapper() uses when it instruments the class" means. I guess my
> >>> question now becomes: How do I add the event.listens_for descriptor to
> >>> the class, since i do not have a class declaration in the traditional
> >>> sense?
>
> >>> On Apr 15, 4:29 pm, Michael Bayer  wrote:
> >>>> @validates hangs a marker of the method that mapper() uses when it 
> >>>> instruments the class, so if the class is already mapped then that train 
> >>>> has left the station.   Taking a cab instead, you can just add the 
> >>>> attribute event directly:
>
> >>>> @event.listens_for(Positive.value, "set")
> >>>> def checkvalue(target, value, oldvalue, initiator)
> >>>>    assert value > 0
>
> >>>> if you want to return a new, mutated value then add retval=True to 
> >>>> listens_for().
>
> >>>> On Apr 15, 2012, at 8:22 AM, lars van gemerden wrote:
>
> >>>>> Hi,
>
> >>>>> I need a way to dynamically add a validates method to a already
> >>>>> created sqla class.
>
> >>>>> In a normal class declaration you can add a validator by:
>
> >>>>> class Positive(Base):
> >>>>>    __tablename__ = "positives"
> >>>>>    value = Column(Integer)
>
> >>>>>    def checkvalue(self, name, value):
> >>>>>        assert value > 0
>

[sqlalchemy] Re: dynamically adding a validates method

[lars van gemerden]

OK, this helps, so how do i do this if i do not know the name of the
attribute to be checked  in advance(the "value" in
@validates("value") )?



On Apr 15, 6:52 pm, Michael Bayer  wrote:
> using type() is equivalent to using a class declaration.   The end result is 
> the same, as are the mechanics of what goes on both from a Python as well as 
> a SQLAlchemy perspective.  So this works:
>
> Positive = type("Positive", (Base,), dict(__tablename__ =
> "positives",  value = Column(Integer)))
>
> @event.listens_for(Positive.value, "set")
> def checkvalue(target, value, oldvalue, initiator)
>    assert value > 0
>
> and also, since type() is equivalent to a class declaration, you can still 
> use @validates,  if you pass the function into the class dictionary, so that 
> it is part of the class before declarative sends it off to mapper():
>
> @validates("value")
> def checkvalue(self, name, value):
>     assert value > 0
>     return value
>
> Positive = type("Positive", (Base,), dict(__tablename__ =
> "positives",  value = Column(Integer), checkvalue=checkvalue))
>
> On Apr 15, 2012, at 12:37 PM, lars van gemerden wrote:
>
>
>
>
>
>
>
> > I don't know what "@validates hangs a marker of the method that
> > mapper() uses when it instruments the class" means. I guess my
> > question now becomes: How do I add the event.listens_for descriptor to
> > the class, since i do not have a class declaration in the traditional
> > sense?
>
> > On Apr 15, 4:29 pm, Michael Bayer  wrote:
> >> @validates hangs a marker of the method that mapper() uses when it 
> >> instruments the class, so if the class is already mapped then that train 
> >> has left the station.   Taking a cab instead, you can just add the 
> >> attribute event directly:
>
> >> @event.listens_for(Positive.value, "set")
> >> def checkvalue(target, value, oldvalue, initiator)
> >>    assert value > 0
>
> >> if you want to return a new, mutated value then add retval=True to 
> >> listens_for().
>
> >> On Apr 15, 2012, at 8:22 AM, lars van gemerden wrote:
>
> >>> Hi,
>
> >>> I need a way to dynamically add a validates method to a already
> >>> created sqla class.
>
> >>> In a normal class declaration you can add a validator by:
>
> >>> class Positive(Base):
> >>>    __tablename__ = "positives"
> >>>    value = Column(Integer)
>
> >>>    def checkvalue(self, name, value):
> >>>        assert value > 0
> >>>        return value
> >>>    validates("value")(checkvalue)
>
> >>> However if you get the class dynamically:
>
> >>> Positive = type("Positive", (Base,), dict(__tablename__ =
> >>> "positives",  value = Column(Integer)))
>
> >>> I can't figure out how to add the validator, either in the type() call
> >>> or afterwards.
>
> >>> Cheers, Lars
>
> >>> --
> >>> You received this message because you are subscribed to the Google Groups 
> >>> "sqlalchemy" group.
> >>> To post to this group, send email to sqlalchemy@googlegroups.com.
> >>> To unsubscribe from this group, send email to 
> >>> sqlalchemy+unsubscr...@googlegroups.com.
> >>> For more options, visit this group 
> >>> athttp://groups.google.com/group/sqlalchemy?hl=en.
>
> > --
> > You received this message because you are subscribed to the Google Groups 
> > "sqlalchemy" group.
> > To post to this group, send email to sqlalchemy@googlegroups.com.
> > To unsubscribe from this group, send email to 
> > sqlalchemy+unsubscr...@googlegroups.com.
> > For more options, visit this group 
> > athttp://groups.google.com/group/sqlalchemy?hl=en.

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[sqlalchemy] Re: dynamically adding a validates method

[lars van gemerden]

I don't know what "@validates hangs a marker of the method that
mapper() uses when it instruments the class" means. I guess my
question now becomes: How do I add the event.listens_for descriptor to
the class, since i do not have a class declaration in the traditional
sense?



On Apr 15, 4:29 pm, Michael Bayer  wrote:
> @validates hangs a marker of the method that mapper() uses when it 
> instruments the class, so if the class is already mapped then that train has 
> left the station.   Taking a cab instead, you can just add the attribute 
> event directly:
>
> @event.listens_for(Positive.value, "set")
> def checkvalue(target, value, oldvalue, initiator)
>    assert value > 0
>
> if you want to return a new, mutated value then add retval=True to 
> listens_for().
>
> On Apr 15, 2012, at 8:22 AM, lars van gemerden wrote:
>
>
>
>
>
>
>
> > Hi,
>
> > I need a way to dynamically add a validates method to a already
> > created sqla class.
>
> > In a normal class declaration you can add a validator by:
>
> > class Positive(Base):
> >    __tablename__ = "positives"
> >    value = Column(Integer)
>
> >    def checkvalue(self, name, value):
> >        assert value > 0
> >        return value
> >    validates("value")(checkvalue)
>
> > However if you get the class dynamically:
>
> > Positive = type("Positive", (Base,), dict(__tablename__ =
> > "positives",  value = Column(Integer)))
>
> > I can't figure out how to add the validator, either in the type() call
> > or afterwards.
>
> > Cheers, Lars
>
> > --
> > You received this message because you are subscribed to the Google Groups 
> > "sqlalchemy" group.
> > To post to this group, send email to sqlalchemy@googlegroups.com.
> > To unsubscribe from this group, send email to 
> > sqlalchemy+unsubscr...@googlegroups.com.
> > For more options, visit this group 
> > athttp://groups.google.com/group/sqlalchemy?hl=en.

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[sqlalchemy] dynamically adding a validates method

[lars van gemerden]

Hi,

I need a way to dynamically add a validates method to a already
created sqla class.

In a normal class declaration you can add a validator by:

class Positive(Base):
__tablename__ = "positives"
value = Column(Integer)

def checkvalue(self, name, value):
assert value > 0
return value
validates("value")(checkvalue)

However if you get the class dynamically:

Positive = type("Positive", (Base,), dict(__tablename__ =
"positives",  value = Column(Integer)))

I can't figure out how to add the validator, either in the type() call
or afterwards.

Cheers, Lars

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[sqlalchemy] Re: append to children in hierarchical data

[lars van gemerden]

The question was based on a misconception on my part  (in a visual
representation of a tree, while dragging a node you drag the whole
subtree with it, so you can't drop a node in it's own subtree).

Sorry about that ...


PS: Checked that when updating the children (via append) the exception
occurs right away (is there a flush happening in the background?),
while when updating the parent, the exception happens during the flush
afterwards.

On Apr 11, 5:41 pm, Michael Bayer  wrote:
> On Apr 11, 2012, at 3:34 AM, lars van gemerden wrote:
>
>
>
>
>
>
>
>
>
> > Hi all,
>
> > I am looking for a way to append a child to a tree like structure. I
> > am using adjacency to represent the tree.
>
> > Let's say I have a relationship configured with:
>
> > children = relationship(TreeNode,
> >                                 primaryjoin = "TreeNode.id ==
> > TreeNode.parent_id",
> >                                 backref = backref( "parent",
> > remote_side=[TreeNode.id]),
> >                                 cascade = "all, delete-orphan",
> >                                 use_list = True)
>
> > and I do:
>
> >   t1 = TreeNode()
> >   t2 = TreeNode(parent = t1)
> >   t3 = TreeNode(parent = t2)
>
> > then i can set:
>
> >   t1.parent = t3,
>
> > without problem, but:
>
> >   t3.children.append(t1)
>
> > gives a CircularDependencyError, while i would like this to give the
> > same result as t1.parent = t3, perhaps by altering the behaviour of
> > Treenode.children.append.
>
> > Am I missing something?
> > Is there some way to arrange for this?
>
> t1.parent = t3 means you aren't persisting a tree anymore - it's no longer a 
> hierarchy, since t3 is a descendant of t1 already via t2.   It's a cycle.
>
> The exception on the "children" side is probably because mutating "children" 
> has the effect of both t3 and t1 being considered in the flush (due to 
> t3.children as well as t1.parent_id changing), whereas t1.parent = t3 does 
> not actually consider "t3" to modified.   You'd still get a cycle if you 
> created everything via "x.parent=y" at once (below I just put it into the 
> adjacency_list.py example - boom):
>
>     node = TreeNode('rootnode')
>     n1 = TreeNode('node1', parent=node)
>     n2 = TreeNode('node2', parent=n1)
>     node.parent = n2
>     session.add(node)
>     session.flush()
>
> sqlalchemy.exc.CircularDependencyError: Circular dependency detected. Cycles: 
>  ...
>
> though I wasn't able to reproduce the behavior being different by mutating 
> children vs. the parentI'm sure with more digging I could figure that 
> out.   But in any case, you aren't safe from cycles if you're building them, 
> the usual way to insert rows with cycles to themselves is to use the 
> post_update feature described 
> athttp://docs.sqlalchemy.org/en/latest/orm/relationships.html#rows-that   
>  You probably need to put it on both sides in this case as the unit of work 
> code will consider one or both of the "children" or "parent" relationships in 
> a particular flush depending on where it sees changes.

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[sqlalchemy] append to children in hierarchical data

[lars van gemerden]

Hi all,

I am looking for a way to append a child to a tree like structure. I
am using adjacency to represent the tree.

Let's say I have a relationship configured with:

children = relationship(TreeNode,
 primaryjoin = "TreeNode.id ==
TreeNode.parent_id",
 backref = backref( "parent",
remote_side=[TreeNode.id]),
 cascade = "all, delete-orphan",
 use_list = True)

and I do:

   t1 = TreeNode()
   t2 = TreeNode(parent = t1)
   t3 = TreeNode(parent = t2)

then i can set:

   t1.parent = t3,

without problem, but:

   t3.children.append(t1)

gives a CircularDependencyError, while i would like this to give the
same result as t1.parent = t3, perhaps by altering the behaviour of
Treenode.children.append.

Am I missing something?
Is there some way to arrange for this?

Cheers, Lars



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[sqlalchemy] Re: help on SAWarning

[lars van gemerden]

Found another bug and the warning is gone; can't pinpoint why
though ...

On Mar 30, 1:03 am, lars van gemerden  wrote:
> OK, thanks, I still get the warning in some cases and i am still
> zooming in on the problem for a small test case.
>
> At least i have solved the problem of the id of InstrumentedLists
> changing after commit(by bypassing one layer of recursion in the xml
> tree parsing, i am not looking up the id of the IList anymore).
> Cheers
>
> On Mar 29, 4:20 pm, Michael Bayer  wrote:
>
>
>
>
>
>
>
> > On Mar 29, 2012, at 9:50 AM, lars van gemerden wrote:
>
> > > I have found that this specific behaviour (re-initialization of the
> > > InstrumentedList) does not happen if "expire_on_commit = False" is set
> > > on the sesssion. However this leads to other errors in my code.
>
> > > I guess I don't quite understand why expire would be called after a
> > > commit; shouldn't the commit result in the session being perfectly
> > > synchronized with the DB?
>
> > It does.  The expire of the attributes doesn't cause any SQL to be emitted 
> > until you access the attributes, in which case a new transaction is begun 
> > (note the DBAPI's default mode of operation is to always be in a 
> > transaction, and SQLAlchemy does not challenge this).  In between your 
> > commit() and the start of a new transaction, any amount of state within the 
> > database may have been changed by other transactions.
>
> > If expire_on_commit=False is leading to errors, that would imply that this 
> > is actually happening in your case.

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[sqlalchemy] Re: return type of relationship

[lars van gemerden]

Thanks,

Is there a more direct way to do this for the Column return type as
well? Now i have:

@staticmethod
def column(cls, name):
for cl in cls.mro():
if hasattr(cl, '__table__'):
for c in cl.__table__.c:
if c.name == name: return c

@staticmethod
def type(obj, name):
try:
return XSALfactory.column(type(obj),
name).type.python_type
except AttributeError:
return type(getattr(obj, name))

(Without the relationship type implemented yet.)


On Mar 30, 1:38 am, Michael Bayer  wrote:
> we're working on a more documented API for getting info like this but at the 
> moment it would be:
>
> MyClass.someattribute.property.mapper.class_
>
> On Mar 29, 2012, at 7:16 PM, lars van gemerden wrote:
>
>
>
>
>
>
>
> > I am generating xml from SAclass objects and need to get the return
> > type (referred SA class)  of an relationship attribute (even if the
> > returned value is None). The type will be used as tagname during XML
> > generation.
>
> > Can anyone tell me how to get this type?
>
> > Cheers, Lars
>
> > --
> > You received this message because you are subscribed to the Google Groups 
> > "sqlalchemy" group.
> > To post to this group, send email to sqlalchemy@googlegroups.com.
> > To unsubscribe from this group, send email to 
> > sqlalchemy+unsubscr...@googlegroups.com.
> > For more options, visit this group 
> > athttp://groups.google.com/group/sqlalchemy?hl=en.

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[sqlalchemy] return type of relationship

[lars van gemerden]

I am generating xml from SAclass objects and need to get the return
type (referred SA class)  of an relationship attribute (even if the
returned value is None). The type will be used as tagname during XML
generation.

Can anyone tell me how to get this type?

Cheers, Lars

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[sqlalchemy] Re: help on SAWarning

[lars van gemerden]

OK, thanks, I still get the warning in some cases and i am still
zooming in on the problem for a small test case.

At least i have solved the problem of the id of InstrumentedLists
changing after commit(by bypassing one layer of recursion in the xml
tree parsing, i am not looking up the id of the IList anymore).
Cheers

On Mar 29, 4:20 pm, Michael Bayer  wrote:
> On Mar 29, 2012, at 9:50 AM, lars van gemerden wrote:
>
> > I have found that this specific behaviour (re-initialization of the
> > InstrumentedList) does not happen if "expire_on_commit = False" is set
> > on the sesssion. However this leads to other errors in my code.
>
> > I guess I don't quite understand why expire would be called after a
> > commit; shouldn't the commit result in the session being perfectly
> > synchronized with the DB?
>
> It does.  The expire of the attributes doesn't cause any SQL to be emitted 
> until you access the attributes, in which case a new transaction is begun 
> (note the DBAPI's default mode of operation is to always be in a transaction, 
> and SQLAlchemy does not challenge this).  In between your commit() and the 
> start of a new transaction, any amount of state within the database may have 
> been changed by other transactions.
>
> If expire_on_commit=False is leading to errors, that would imply that this is 
> actually happening in your case.

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[sqlalchemy] Re: help on SAWarning

[lars van gemerden]

I have found that this specific behaviour (re-initialization of the
InstrumentedList) does not happen if "expire_on_commit = False" is set
on the sesssion. However this leads to other errors in my code.

I guess I don't quite understand why expire would be called after a
commit; shouldn't the commit result in the session being perfectly
synchronized with the DB?



On Mar 29, 12:48 pm, lars van gemerden  wrote:
> I think I have an odd case of the first possibility you mentioned:
>
> I am generating XML from SAclass objects opdating these objects from
> XML. To detect cyclic references and double objects, I maintain a
> registry of objects based on id() (reg[str(id(obj))] = obj). The id is
> stored as the attribute "ID" in the XML tag. When updating the objects
> I first look them up in the registry obj = reg[etree.get("ID")] and
> update them afterwards. I do this as well with relationships/
> InstrumentedLists (but not with database fields like Integer).
>
> What I noticed was that InstrumentedList changes id() after a commit
> (with a = Address(), Address.persons = relationship(...) ):
>
>     print id(a), id(a.persons), id(a.persons[0])
>     session.commit()
>     print id(a), id(a.persons), id(a.persons[0])
>
> gives:
>
> 47148168 47174264 47114112
> 47148168 47175784 47114112 (the middle id has changed)
>
> So I assume that after a commit a new InstrumentedList is created.
>
> - Could it be conceivable that is causes the warning mentioned
> above(an old version of the InstrumentedList being updated with an
> valid SAclass object)?
> - Is there a way to get around this new INstrumetnedList being
> created?
>
> Cheers, Lars
>
> On Mar 29, 1:53 am, Michael Bayer  wrote:
>
>
>
>
>
>
>
> > you've got a situation like this:
>
> > ft = session.query(FieldType).first()
>
> > f = Field()
> > ft.of_members.append(f)
>
> > assert f in session  # normally returns True, assuming normal cascade on 
> > "of_members"
>
> > session.expunge(f)  # remove f from the session
>
> > session.flush()   # generates warning, since ft.of_members has changed but 
> > the contents aren't in the Session
>
> > Another cause could be, "of_members" has a cascade that doesn't include 
> > save-update, like "cascade='delete'" is a common mistake.
>
> > On Mar 28, 2012, at 6:45 PM, lars van gemerden wrote:
>
> > > Hi all,
>
> > > I am getting the error: "SAWarning: Object of type  not in
> > > session, add operation along 'FieldType.of_members' will not proceed"
> > > and have no idea where to start looking for the error. Can anyone help
> > > me with some idea of why this warning occurs or what direction to look
> > > in order to fix it?
>
> > > The warning occurs only during the first call of a specific method,
> > > while i think i reset everything (e.g. dropping all tables in the
> > > database) between calls.
>
> > > Cheers, Lars
>
> > > --
> > > You received this message because you are subscribed to the Google Groups 
> > > "sqlalchemy" group.
> > > To post to this group, send email to sqlalchemy@googlegroups.com.
> > > To unsubscribe from this group, send email to 
> > > sqlalchemy+unsubscr...@googlegroups.com.
> > > For more options, visit this group 
> > > athttp://groups.google.com/group/sqlalchemy?hl=en.

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[sqlalchemy] Re: help on SAWarning

[lars van gemerden]

I think I have an odd case of the first possibility you mentioned:

I am generating XML from SAclass objects opdating these objects from
XML. To detect cyclic references and double objects, I maintain a
registry of objects based on id() (reg[str(id(obj))] = obj). The id is
stored as the attribute "ID" in the XML tag. When updating the objects
I first look them up in the registry obj = reg[etree.get("ID")] and
update them afterwards. I do this as well with relationships/
InstrumentedLists (but not with database fields like Integer).

What I noticed was that InstrumentedList changes id() after a commit
(with a = Address(), Address.persons = relationship(...) ):

print id(a), id(a.persons), id(a.persons[0])
session.commit()
print id(a), id(a.persons), id(a.persons[0])

gives:

47148168 47174264 47114112
47148168 47175784 47114112 (the middle id has changed)

So I assume that after a commit a new InstrumentedList is created.

- Could it be conceivable that is causes the warning mentioned
above(an old version of the InstrumentedList being updated with an
valid SAclass object)?
- Is there a way to get around this new INstrumetnedList being
created?

Cheers, Lars



On Mar 29, 1:53 am, Michael Bayer  wrote:
> you've got a situation like this:
>
> ft = session.query(FieldType).first()
>
> f = Field()
> ft.of_members.append(f)
>
> assert f in session  # normally returns True, assuming normal cascade on 
> "of_members"
>
> session.expunge(f)  # remove f from the session
>
> session.flush()   # generates warning, since ft.of_members has changed but 
> the contents aren't in the Session
>
> Another cause could be, "of_members" has a cascade that doesn't include 
> save-update, like "cascade='delete'" is a common mistake.
>
> On Mar 28, 2012, at 6:45 PM, lars van gemerden wrote:
>
>
>
>
>
>
>
> > Hi all,
>
> > I am getting the error: "SAWarning: Object of type  not in
> > session, add operation along 'FieldType.of_members' will not proceed"
> > and have no idea where to start looking for the error. Can anyone help
> > me with some idea of why this warning occurs or what direction to look
> > in order to fix it?
>
> > The warning occurs only during the first call of a specific method,
> > while i think i reset everything (e.g. dropping all tables in the
> > database) between calls.
>
> > Cheers, Lars
>
> > --
> > You received this message because you are subscribed to the Google Groups 
> > "sqlalchemy" group.
> > To post to this group, send email to sqlalchemy@googlegroups.com.
> > To unsubscribe from this group, send email to 
> > sqlalchemy+unsubscr...@googlegroups.com.
> > For more options, visit this group 
> > athttp://groups.google.com/group/sqlalchemy?hl=en.

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[sqlalchemy] help on SAWarning

[lars van gemerden]

Hi all,

I am getting the error: "SAWarning: Object of type  not in
session, add operation along 'FieldType.of_members' will not proceed"
and have no idea where to start looking for the error. Can anyone help
me with some idea of why this warning occurs or what direction to look
in order to fix it?

 The warning occurs only during the first call of a specific method,
while i think i reset everything (e.g. dropping all tables in the
database) between calls.

Cheers, Lars

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[sqlalchemy] Re: names of foreign keys from unknown table/class (short question)

[lars van gemerden]

Thanks you Michael (i thought i remembered that the name attribute of
the column wasn't set unless explicitely given to the Column
constructor, the one thing i didn't check ... )



On Mar 26, 3:55 pm, Michael Bayer  wrote:
> Column has a collection "foreign_keys", a collection since a column in a 
> relational database can have any number of foreign key constraints applied to 
> it.  If this collection is non-empty, then that Column is associated with a 
> ForeignKey and thus a ForeignKeyConstraint (note that a ForeignKey is 
> ultimately an element in a larger ForeignKeyConstraint object).
>
> Not sure what you mean by the "name" - assuming you mean the name of the 
> column it refers to, ForeignKey has an accessor ".column" that will give you 
> the Column to which it refers to:
>
> http://docs.sqlalchemy.org/en/latest/core/schema.html?highlight=forei...
>
> That gives you the Column itself with a ".name" attribute.
>
> If by "name" you mean the name of the constraint itself, like for the 
> purposes of "ADD CONSTRAINT/DROP CONSTRAINT", the ForeignKey object of each 
> Column is by default unnamed - in relational DDL, you don't need to give 
> explicit names to FK constraints, the database will name these automatically. 
>  So unless you give them a name, the name can't be determined on the Python 
> side.  When reflecting a table, the ForeignKeyConstraint is reflected along 
> with the name, if the database supports giving us the name, and the name 
> should be associated with each associated ForeignKey object.
>
> On Mar 25, 2012, at 7:29 PM, lars van gemerden wrote:
>
>
>
>
>
>
>
> > Hello,
>
> > Does anyone know a way get the names of the foreign key columns of a
> > table, if the table/class is unknown beforehand?
>
> > I tried with "Column.foreign_keys", which gives a set (why?) of
> > "ForeignKey" objects but the "name" attribute of "ForeignKey"  is not
> > automatically set.
>
> > Cheers, Lars
>
> > --
> > You received this message because you are subscribed to the Google Groups 
> > "sqlalchemy" group.
> > To post to this group, send email to sqlalchemy@googlegroups.com.
> > To unsubscribe from this group, send email to 
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[sqlalchemy] Re: xml approach

[lars van gemerden]

Using some of your example, together with code i wrote to XMLify
simple python classes (like pickle, but xml out.input) I have got
something working that handles circular references and updates the
database after XML has been changed(e.g. in a client) and parsed
back.

It creates a reference dict with python function id(obj) as key
(registry[id(obj)] = obj) to later see whether an object has already
been written to or read from the XML string. This id is stored in the
XML tag ( something ). If the id is
already in the registry, it will write new occurences of obj as
. When the xml is read, basically the same
registry is created and used to look up objects that have been created
already.

I also stores the primary key(s) as XML attribute ( something ) to be able to look up the correct
database entry to be updated when the XML is read back
(session.query(cls).get(eval(element.get("PK")))..

The result looks something like this:


 1 
 bla bla 



 1 
 1 
 john 




(xml attribute "name" is the name of the attribute)

If there is any interest i will post a sqlalchemy specific version of
the code, when it is somewhat ready.

Cheers, Lars

On Mar 26, 10:16 am, Julien Cigar  wrote:
> On 03/23/2012 10:37, lars van gemerden wrote:
>
> > Hi Julian,
>
> > Thanks, I am looking into it and it looks interesting. Have you done
> > much testing yet? How do you (plan to; haven't looked at too much
> > detail yet) check for circular references (like backrefs)?
>
> circular references aren't handled yet .. at the moment all what you can
> do is something like:
>
>  >>> a = Page.query.get(454)
>
>  >>> SAMappedSerializer(a).json(exclude_columns=('body', ),
> include_relations=('type', 'tags'))
> '{"updated": "2012-03-21T16:52:43Z", "added": "2009-10-16T14:23:24Z",
> "description": "The Belgian Biodiversity Platform", "effective": null,
> "tags": [{"description": null, "id": 26, "name": "Belspo"},
> {"description": null, "id": 29, "name": "Belgian Biodiversity
> Platform"}], "icon_content_id": null, "count_children": 0, "customized":
> false, "weight": 23, "owner_id": 1, "content_id": 454, "expiration":
> null, "polymorphic_loading": null, "state_id": 3, "title": "About us",
> "exclude_nav": false, "type": {"description": null, "icon": "page.png",
> "id": 2, "name": "page"}, "id": 454, "container_id": 1,
> "content_type_id": 2}'
>
>  >>> SAMappedSerializer(a).xml(exclude_columns=('body', ),
> include_relations=('type', 'tags'))
> 2012-03-21T16:52:43Z2009-10-16T14:23:24Z 
> The
> Belgian Biodiversity Platform /> />26Belspo />29Belgian Biodiversity
> Platform />0False2 
> 31454 />3About
> usFalse />page.png2page454 iner_id>12
>
> etc
>
>
>
>
>
>
>
>
>
> > Cheers, Lars
>
> > On Thursday, March 22, 2012 11:36:41 AM UTC+1, lars van gemerden wrote:
>
> >     Hi,
>
> >     I am looking for a way to convert SQLalchemy objects to XML and
> >     back, in order to support a webapplication. I made a mixin class
> >     that does a decent job on 'normal' python objects (basically works
> >     for in the same cases as pickle, though more testing is required).
> >     I would prefer to have a simple mixin interface with something like:
>
> >     def toXML():
> >         'convert attributes to xml'
> >         return xmlstring
>
> >     def fromXML(xmlstring)
> >         'update attributes from xml'
>
> >     The most simple case would be that the web user request indicates
> >     the primary key of the object, gets the corrsponding xml string in
> >     return, changes fields in the xml string and posts it back, which
> >     leads to an update of the object.
>
> >     I have formulated a couple of initial questions:
>
> >     -  what attributes should be converted to and from xml?
> >     -  how do i handle foreign keys on the 'other' side?
>
> >     Note that the object remains in memory during the user
> >     interaction, so it does not have to be reinitialized from scratch.
>
> >     Cheers, Lars
>
> 

[sqlalchemy] Re: names of foreign keys from unknown table/class (short question)

[lars van gemerden]

I must be missing something simple:

i have looked in:

 - orm.properties.ColumnProperty (which i iterate by name using
mapper.iterate_properties); couldn't find anything about foreign keys
or the originating Column
 - Column (iterate via class.__table__.c); can see whether it is a
Foreign key, but not always the name of the column
 - class.__dict__; cannot address the Columns by name (they are in
__table__)
 - orm.attributes.InstrumentedAttribute via class.__dict__: could not
find anything about foreign keys or related column.

I am working on a way to translate SQLA objects to XML, but do not
always want to include the FK's (instead include the "relationship"
attribute values)

What am I missing?

Cheers, Lars

On Mar 26, 1:29 am, lars van gemerden  wrote:
> Hello,
>
> Does anyone know a way get the names of the foreign key columns of a
> table, if the table/class is unknown beforehand?
>
> I tried with "Column.foreign_keys", which gives a set (why?) of
> "ForeignKey" objects but the "name" attribute of "ForeignKey"  is not
> automatically set.
>
> Cheers, Lars

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[sqlalchemy] names of foreign keys from unknown table/class (short question)

[lars van gemerden]

Hello,

Does anyone know a way get the names of the foreign key columns of a
table, if the table/class is unknown beforehand?

I tried with "Column.foreign_keys", which gives a set (why?) of
"ForeignKey" objects but the "name" attribute of "ForeignKey"  is not
automatically set.

Cheers, Lars

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[sqlalchemy] Re: short question about primary keys

[lars van gemerden]

Perfect, thank you!

On Mar 23, 10:09 pm, Benjamin Trofatter 
wrote:
> Not knowing the names of the primary keys shouldn't be a problem since
> they're pretty easy to figure out with the object_mapper.
>
> from sqlalchemy.orm import object_mapper
>
> class MyMixin(object):
>
>     def get_pk(self):
>         om = object_mapper(self)
>         keys = [k.key for k in om.primary_key]
>         return tuple(getattr(self, k) for k in keys)
>
> On Fri, Mar 23, 2012 at 2:48 PM, lars van gemerden 
> wrote:
>
>
>
>
>
>
>
> > Hi,
>
> > Does anyone know a way get the the value(s) of the primary key(s), if
> > you don't know the name of the primary key column(s). This to be used
> > in a mixin class that can be used for different tables/classes.
>
> > Cheers, Lars
>
> > --
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> > To unsubscribe from this group, send email to
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[sqlalchemy] short question about primary keys

[lars van gemerden]

Hi,

Does anyone know a way get the the value(s) of the primary key(s), if
you don't know the name of the primary key column(s). This to be used
in a mixin class that can be used for different tables/classes.

Cheers, Lars

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[sqlalchemy] Re: xml approach

[lars van gemerden]

Hi Julian,

Thanks, I am looking into it and it looks interesting. Have you done much 
testing yet? How do you (plan to; haven't looked at too much detail yet) 
check for circular references (like backrefs)?

Cheers, Lars

On Thursday, March 22, 2012 11:36:41 AM UTC+1, lars van gemerden wrote:
>
> Hi,
>
> I am looking for a way to convert SQLalchemy objects to XML and back, in 
> order to support a webapplication. I made a mixin class that does a decent 
> job on 'normal' python objects (basically works for in the same cases as 
> pickle, though more testing is required). I would prefer to have a simple 
> mixin interface with something like:
>
> def toXML(): 
> 'convert attributes to xml'
> return xmlstring
>
> def fromXML(xmlstring)
> 'update attributes from xml'
>
> The most simple case would be that the web user request indicates the 
> primary key of the object, gets the corrsponding xml string in return, 
> changes fields in the xml string and posts it back, which leads to an 
> update of the object. 
>
> I have formulated a couple of initial questions:
>
> -  what attributes should be converted to and from xml?
> -  how do i handle foreign keys on the 'other' side?
>
> Note that the object remains in memory during the user interaction, so it 
> does not have to be reinitialized from scratch.
>
> Cheers, Lars
>
>  
>

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[sqlalchemy] xml approach

[lars van gemerden]

Hi,

I am looking for a way to convert SQLalchemy objects to XML and back, in 
order to support a webapplication. I made a mixin class that does a decent 
job on 'normal' python objects (basically works for in the same cases as 
pickle, though more testing is required). I would prefer to have a simple 
mixin interface with something like:

def toXML(): 
'convert attributes to xml'
return xmlstring

def fromXML(xmlstring)
'update attributes from xml'

The most simple case would be that the web user request indicates the 
primary key of the object, gets the corrsponding xml string in return, 
changes fields in the xml string and posts it back, which leads to an 
update of the object. 

I have formulated a couple of initial questions:

-  what attributes should be converted to and from xml?
-  how do i handle foreign keys on the 'other' side?

Note that the object remains in memory during the user interaction, so it 
does not have to be reinitialized from scratch.

Cheers, Lars

 

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[sqlalchemy] Re: short drop_all question

[lars van gemerden]

I can see that being true in the general case, and at some point i
will start working with a serious database, but at the moment i am
working on a prototype (in which db persistance is maybe a quarter of
the work), still have a long list of items to implement and was hoping
to abstract away from sql and database specifics with sqlalchemy.

Cheers, Lars

On Feb 28, 11:30 am, Chris Withers  wrote:
> On 25/02/2012 11:07, lars van gemerden wrote:
>
> > Actually, now I think about it, i had a couple of reasons:
>
> > - easy to start with (no separeate installation is i remember
> > correctly)
>
> ...but bear in mind that it's a very weak database in terms of
> functionality...
>
> > - no decision required about which database (mysql, postgress) to
> > learn
>
> That's not true, you're choosing to learn sqlite, which isn't likely to
> be useful for any real world projects.
>
> > - no problem with removal of database (in memory), but that is between
> > runs, not during unit testing
>
> There's no problem deleting databases with any rbms provided your user
> has the right privileges.
>
> > Main reason that i want to remove the database, is that i create
> > tables dynamically, from another database with table definitions. To
> > run multiple tests I need to clear the database in between.
>
> I used to think that sqlite was good for testing too, it really isn't.
> I've learned the error of my ways and you should too ;-)
>
> Do some research, decide which database you want to use and develop and
> test against that. Yes, SQL is supposed to be the panacea that abstracts
> away from the rdbms, but that's a lie...
>
> Chris
>
> --
> Simplistix - Content Management, Batch Processing & Python Consulting
>              -http://www.simplistix.co.uk

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[sqlalchemy] Re: deleting a sqlite database

[lars van gemerden]

Thank you very much again .. that worked like a charm.

For future reference, to give some idea, this is the function i now
use to generate the root base table/class for the generated joined
class inheritance tree:

def createObject():
dct = dict(association_tables = {},
   __tablename__ = 'Object',
   id = Column(Integer, primary_key = True),
   type_name = Column(String(50),
ForeignKey(datatypes.Type.__table__.c.name), nullable = False, default
= 'Object'),
   created_at = Column(DateTime, default = func.now()),
   __mapper_args__ = {'polymorphic_on': 'type_name'},
   type = relationship(datatypes.Type, uselist = False))
return type('Object', (declarative_base(bind = datatypes.engine),
MethodMixin), dct)

with datatypes.Type the main class/table holding the generated class/
table parameters, MethodMixin holding some extra methods (like
__repr__), association_tables holding the associations for many-to-
many relationships  (still to be tested). Classes and corresponding
tables are named the same.

I haven't tested much, but for now everything seems to work. Note that
each time this function runs, an new 'Base' class is created for the
generated class 'Object'.

Questions are very welcome.

Cheers, Lars



On Feb 27, 4:28 pm, Michael Bayer  wrote:
> >> The only database link between these two sets is the 'polymorphic on'
> >> column in the root base table in set 2, which is a foreign key to a
> >> Type table in set 1.
>
> also, I'd set up this foreign key using a literal Column so you don't have to 
> worry about string lookups:
>
> ForeignKey(MyRoot.__table__.c.type)
>
> and definitely don't make any backrefs into the fixed system !   Otherwise 
> then yes we might have to look at clearing out mappers entirely between tests.
>
>
>
>
>
>
>
>
>
> >> For a typical test i would like to:
>
> >> 1) create records in set 1 of tables (representing classes/tables with
> >> their attributes/foreign keys and fields),
> >> 2) from these records generate the tables/classes, where the tables
> >> will be in set 2.
> >> 3) add records to the generated tables/classes and test whether
> >> adding, updating, deleting and querying works as intended.
>
> >> To be able to perform multiple of these tests in one run, i need to
> >> empty the tables of set 1. However i need to completely remove any
> >> data (mappings, class definitions, records, tables) from set 2,
> >> between individual tests.
>
> > so what I would do is:
>
> > 1. the "other tables" generated would be in their own MetaData object.  
> > After you've done drop_all() for those, throw that whole MetaData away.
> > 2. the "other classes" generated, I'm assuming these are generated as the 
> > result of some function being called and aren't declared within a module.   
> > When you're done with them, throw them away too.
> > 3. The next run of tests would redo the entire process, using a new 
> > MetaData object, and generating new classes.
>
> > Key here is that there's no point at which the dynamically generated 
> > classes/tables/mappers need to be present as de-composed elements, once 
> > they've been composed.   They're just thrown away.
>
> > Using two Base classes would be an easy way to achieve this.
>
> >> I (naively) thought of some ways this might be possible:
>
> >> 1) use two separate metadata objects for the same database, bind them
> >> to separate 'Base' classes, one for each set  and replace the one
> >> representing set 2 before each individual test,
> >> 2) find some way to remove all data concerning set 2 of tables from
> >> mappings, metadata, database, etc. between tests,
> >> 3) use two databases, one for each set of tables and forego the
> >> foreign key realtionship between then (or maybe copy set 1 to the
> >> second database)
>
> >> Please advise on which of these approaches are possible, more
> >> straightforward, ... or whether another approach might be more
> >> appropriate.
>
> >> Cheers, Lars
>
> >> On Feb 26, 10:47 pm, Michael Bayer  wrote:
> >>> On Feb 26, 2012, at 12:47 PM, lars van gemerden wrote:
>
> >>>> I was wrong, the method emptied the database, but I was checking the
> >>>> tables in the metadata.
>
> >>>> This time I am also removing the tables from the metadata, but if i
> >>>> generate the same 

[sqlalchemy] Re: deleting a sqlite database

[lars van gemerden]

Thank you for the extensive reply. It makes things a lot clearer;
still i am not sure about how to continue.

Conceptually i would like to create 2 sets of tables/classes in a
database (as part of a prototype):

1) one set of tables/classes with the parameters to generate other
classes/tables from,
2) one set of tables/classes that is automatically generated from the
parameters in the first set. It will feature joined inheritance with
only one root base table/class.

The only database link between these two sets is the 'polymorphic on'
column in the root base table in set 2, which is a foreign key to a
Type table in set 1.

For a typical test i would like to:

1) create records in set 1 of tables (representing classes/tables with
their attributes/foreign keys and fields),
2) from these records generate the tables/classes, where the tables
will be in set 2.
3) add records to the generated tables/classes and test whether
adding, updating, deleting and querying works as intended.

To be able to perform multiple of these tests in one run, i need to
empty the tables of set 1. However i need to completely remove any
data (mappings, class definitions, records, tables) from set 2,
between individual tests.

I (naively) thought of some ways this might be possible:

1) use two separate metadata objects for the same database, bind them
to separate 'Base' classes, one for each set  and replace the one
representing set 2 before each individual test,
2) find some way to remove all data concerning set 2 of tables from
mappings, metadata, database, etc. between tests,
3) use two databases, one for each set of tables and forego the
foreign key realtionship between then (or maybe copy set 1 to the
second database)

Please advise on which of these approaches are possible, more
straightforward, ... or whether another approach might be more
appropriate.

Cheers, Lars







On Feb 26, 10:47 pm, Michael Bayer  wrote:
> On Feb 26, 2012, at 12:47 PM, lars van gemerden wrote:
>
> > I was wrong, the method emptied the database, but I was checking the
> > tables in the metadata.
>
> > This time I am also removing the tables from the metadata, but if i
> > generate the same tables in two separate test methods (with a call to
> > tearDown ans setUp in between), I still get an error about a backref
> > name on a relationship already existing.
>
> OK I think you're mixing concepts up here, a backref is an ORM concept.  The 
> Table and Metadata objects are part of Core and know absolutely nothing about 
> the ORM or mappings.    Removing a Table from a particular MetaData has 
> almost no effect as all the ORM mappings still point to it.  In reality the 
> MetaData.remove() method is mostly useless, except that a create_all() will 
> no longer hit that Table, foreign key references will no longer find it, and 
> you can replace it with a new Table object of the same name, but again 
> nothing to do with the ORM and nothing to do with the state of that removed 
> Table, which still points to that MetaData and will otherwise function 
> normally.
>
> If you want to remove mappings, you can call clear_mappers().  The use case 
> for removing individual mappers is not supported as there is no support for 
> doing all the reverse bookkeeping of removing relationships(), backrefs, and 
> inheritance structures, and there's really no need for such a feature.
>
> Like MetaData.remove(), there's almost no real world use case for 
> clear_mappers() except that of the SQLAlchemy unit tests themselves, or tests 
> of other ORM-integration layers like Elixir, which are testing the ORM itself 
> with various kinds of mappings against the same set of classes.
>
> Unit tests in an outside world application would normally be against a schema 
> that's an integral part of the application, and doesn't change with regards 
> to classes.   There's virtually no reason in normal applications against a 
> fixed schema to tear down mappings and table metadata between tests.    
> SQLAlchemy docs stress the Declarative pattern very much these days as we're 
> really trying to get it across that the composition of class, table metadata, 
> and mapping is best regarded as an atomic structure - it exists only as that 
> composite, or not at all.   Breaking it apart has little use unless you're 
> testing the mechanics of the mapping itself.
>
> Throughout all of this, we are *not* talking about the tables and schema that 
> are in the actual database.   It is typical that unit tests do drop all those 
> tables in between test suites, and recreate them for another test suite.    
> Though I tend to favor not actually dropping / recreating and instead running 
> the tests within a transaction that's rolled back at the end as it's much

[sqlalchemy] Re: deleting a sqlite database

[lars van gemerden]

I was wrong, the method emptied the database, but I was checking the
tables in the metadata.

This time I am also removing the tables from the metadata, but if i
generate the same tables in two separate test methods (with a call to
tearDown ans setUp in between), I still get an error about a backref
name on a relationship already existing. If I run the same two tests
in separate runs the error does not occur and from that i conclude
that somehow the metadata retains the class definitions. My tearDown
and setUp are:

class SQLAtest(unittest.TestCase):

def setUp(self):
Base.metadata.create_all(engine)
self.session = Session()

def tearDown(self):
self.session.close()
tools.drop_tables(Base.metadata, engine, excludes)

with tools.drop_tables removing all tables from the database (using
the DropEverything function) and all tables except from the excludes
from the metadata (with metadata.remove(table) ).

Some tables (with class definitions) are defined in modules, while
others are generated on the flight (from the class definitions). From
the first i just want to remove the records (or regenerate the tables
from the existing metadata), while the others i want to remove
completely.

I have also considered creating new metadata in setUp, but i would not
know how to reinitialize it with the classes/tables hard coded in the
modules.

Is there a way to achieve this or am i missing something?

Cheers, Lars


On Feb 25, 3:46 pm, Michael Bayer  wrote:
> On Feb 25, 2012, at 6:57 AM, lars van gemerden wrote:
>
> > Hi all,
>
> > I looking for a way to delete/empty a sqlite database completely (can
> > be in memory or file). I have tried:
>
> > - metadata.drop_all(engine); which does not work with cyclic
> > references
>
> The cycles here are only between the ForeignKey objects themselves, in 
> Python.   SQLite doesn't care.   Add the use_alter=True flag to each 
> ForeignKey in a cycle.
>
> > - solution 
> > fromhttp://www.sqlalchemy.org/trac/wiki/UsageRecipes/DropEverything;
> > it requires names of foreign key columns to be returned by the
> > inspector class, however these names are empty
>
> are you using "PRAGMA foreign_keys = ON" ?      I've run this recipe with 
> that flag on and off and while it doesn't get the foreign key constraints 
> explicitly, it still drops all the tables just fine.    Perhaps I'm not 
> actually achieving the "foreign_keys=ON" part since SQLite still lets me drop 
> a table that others are dependent on.

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[sqlalchemy] deleting a sqlite database

[lars van gemerden]

Hi all,

I looking for a way to delete/empty a sqlite database completely (can
be in memory or file). I have tried:

- metadata.drop_all(engine); which does not work with cyclic
references

- solution from http://www.sqlalchemy.org/trac/wiki/UsageRecipes/DropEverything;
it requires names of foreign key columns to be returned by the
inspector class, however these names are empty

- some other ways.

I am unittesting dynamic generation of tables/classes dynamically from
definitions in another database. To be able to run multiple tests in
one run, my tearDown method must delete/empty the database.

Any tips or solutions? Have I overlooked something obvious?  It seems
that it should not be that complicated.

Cheers, Lars

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[sqlalchemy] deleting a sqlite database

[lars van gemerden]

Hi all,

I looking for a way to delete/empty a sqlite database completely (can
be in memory or file). I have tried:

- metadata.drop_all(engine); which does not work with cyclic
references

- solution from http://www.sqlalchemy.org/trac/wiki/UsageRecipes/DropEverything;
it requires names of foreign key columns to be returned by the
inspector class, however these names are empty

- some other ways.

I am unittesting dynamic generation of tables/classes dynamically from
definitions in another database. To be able to run multiple tests in
one run, my tearDown method must delete/empty the database.

Any tips or solutions? Have I overlooked something obvious?  It seems
that it should not be that complicated.

Cheers, Lars

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[sqlalchemy] Re: short drop_all question

[lars van gemerden]

Actually, now I think about it, i had a couple of reasons:

- easy to start with (no separeate installation is i remember
correctly)
- no decision required about which database (mysql, postgress) to
learn
- no problem with removal of database (in memory), but that is between
runs, not during unit testing

Main reason that i want to remove the database, is that i create
tables dynamically, from another database with table definitions. To
run multiple tests I need to clear the database in between.

Lars


On Feb 24, 5:14 pm, Chris Withers  wrote:
> Why are you testing with sqlite?
>
> Chris
>
> On 24/02/2012 14:32, lars van gemerden wrote:
>
>
>
>
>
>
>
>
>
> > OK, the file isn't closed ofcourse and i can't figure out how to close
> > it. I'll try some more and if nothing works probably start a new
> > post ...
>
> > Thanks anyway, Chris
>
> > On Feb 24, 3:02 pm, lars van gemerden  wrote:
> >> The recipe didn't work; it collects all tables, but no foreign keys
> >> and in the end removes nothing.
>
> >> I am using this in tearDown of unit tests. I have the DB in memory and
> >> even create a new engine in setUp ... maybe I am overlooking somthing
> >> dumb, but I don't get it.
>
> >> I'll try using a sqlite file and closing and deleting the file in
> >> tearDown.
>
> >> Cheers, Lars
>
> >> On Feb 24, 2:28 pm, lars van gemerden  wrote:
>
> >>> Thanks very much,
>
> >>> Nothing is ever easy ... :-(
>
> >>> why not .. :-)
>
> >>> On Feb 24, 2:11 pm, Chris Withers  wrote:
>
> >>>> On 24/02/2012 12:40, lars van gemerden wrote:
>
> >>>>> can it be possible that drop_all does not empty the database of there
> >>>>> are circular references between tables?
>
> >>>> You want:
>
> >>>>http://www.sqlalchemy.org/trac/wiki/UsageRecipes/DropEverything
>
> >>>> ...which is available here too:
>
> >>>>http://packages.python.org/mortar_rdb/api.html#mortar_rdb.drop_tables
>
> >>>> cheers,
>
> >>>> Chris
>
> >>>> PS:
>
> >>>>> I am using sqlite.
>
> >>>> Why? ;-)
>
> >>>> --
> >>>> Simplistix - Content Management, Batch Processing&  Python Consulting
> >>>>               -http://www.simplistix.co.uk
>
> --
> Simplistix - Content Management, Batch Processing & Python Consulting
>              -http://www.simplistix.co.uk

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[sqlalchemy] Re: short drop_all question

[lars van gemerden]

OK, the file isn't closed ofcourse and i can't figure out how to close
it. I'll try some more and if nothing works probably start a new
post ...

Thanks anyway, Chris

On Feb 24, 3:02 pm, lars van gemerden  wrote:
> The recipe didn't work; it collects all tables, but no foreign keys
> and in the end removes nothing.
>
> I am using this in tearDown of unit tests. I have the DB in memory and
> even create a new engine in setUp ... maybe I am overlooking somthing
> dumb, but I don't get it.
>
> I'll try using a sqlite file and closing and deleting the file in
> tearDown.
>
> Cheers, Lars
>
> On Feb 24, 2:28 pm, lars van gemerden  wrote:
>
>
>
>
>
>
>
> > Thanks very much,
>
> > Nothing is ever easy ... :-(
>
> > why not .. :-)
>
> > On Feb 24, 2:11 pm, Chris Withers  wrote:
>
> > > On 24/02/2012 12:40, lars van gemerden wrote:
>
> > > > can it be possible that drop_all does not empty the database of there
> > > > are circular references between tables?
>
> > > You want:
>
> > >http://www.sqlalchemy.org/trac/wiki/UsageRecipes/DropEverything
>
> > > ...which is available here too:
>
> > >http://packages.python.org/mortar_rdb/api.html#mortar_rdb.drop_tables
>
> > > cheers,
>
> > > Chris
>
> > > PS:
>
> > > > I am using sqlite.
>
> > > Why? ;-)
>
> > > --
> > > Simplistix - Content Management, Batch Processing & Python Consulting
> > >              -http://www.simplistix.co.uk

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[sqlalchemy] Re: short drop_all question

[lars van gemerden]

The recipe didn't work; it collects all tables, but no foreign keys
and in the end removes nothing.

I am using this in tearDown of unit tests. I have the DB in memory and
even create a new engine in setUp ... maybe I am overlooking somthing
dumb, but I don't get it.

I'll try using a sqlite file and closing and deleting the file in
tearDown.

Cheers, Lars

On Feb 24, 2:28 pm, lars van gemerden  wrote:
> Thanks very much,
>
> Nothing is ever easy ... :-(
>
> why not .. :-)
>
> On Feb 24, 2:11 pm, Chris Withers  wrote:
>
>
>
>
>
>
>
> > On 24/02/2012 12:40, lars van gemerden wrote:
>
> > > can it be possible that drop_all does not empty the database of there
> > > are circular references between tables?
>
> > You want:
>
> >http://www.sqlalchemy.org/trac/wiki/UsageRecipes/DropEverything
>
> > ...which is available here too:
>
> >http://packages.python.org/mortar_rdb/api.html#mortar_rdb.drop_tables
>
> > cheers,
>
> > Chris
>
> > PS:
>
> > > I am using sqlite.
>
> > Why? ;-)
>
> > --
> > Simplistix - Content Management, Batch Processing & Python Consulting
> >              -http://www.simplistix.co.uk

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[sqlalchemy] Re: short drop_all question

[lars van gemerden]

Thanks very much,

Nothing is ever easy ... :-(

why not .. :-)

On Feb 24, 2:11 pm, Chris Withers  wrote:
> On 24/02/2012 12:40, lars van gemerden wrote:
>
> > can it be possible that drop_all does not empty the database of there
> > are circular references between tables?
>
> You want:
>
> http://www.sqlalchemy.org/trac/wiki/UsageRecipes/DropEverything
>
> ...which is available here too:
>
> http://packages.python.org/mortar_rdb/api.html#mortar_rdb.drop_tables
>
> cheers,
>
> Chris
>
> PS:
>
> > I am using sqlite.
>
> Why? ;-)
>
> --
> Simplistix - Content Management, Batch Processing & Python Consulting
>              -http://www.simplistix.co.uk

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[sqlalchemy] short drop_all question

[lars van gemerden]

can it be possible that drop_all does not empty the database of there
are circular references between tables?

I am using sqlite.

Cheers, Lars

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[sqlalchemy] Re: order of initialization __mapper_args__ 'inherit_condition' and primary key

[lars van gemerden]

Yep, they are the same class (i don't create any class of which i
don't have the superclass yet).

Thanks for your help; on to the next bug ...

On Feb 23, 5:32 pm, Michael Bayer  wrote:
> On Feb 23, 2012, at 10:47 AM, lars van gemerden wrote:
>
>
>
>
>
>
>
>
>
> > OK, thanks, the order wasn't the problem, I am using this for the
> > initialization of my classes:
>
> >    dicty= {'__tablename__': name,
> >           'id': Column(Integer, ForeignKey(basename + '.id'),
> > primary_key = True),
> >           '__mapper_args__': {'polymorphic_identity': name,
> > 'inherit_condition': (id == classes[basename].id)}}
>
> > and as you said 'id' in the last line refers to the id() function. I
> > think I fixed it by changing the code to:
>
> >    id_ = Column(Integer, ForeignKey(basename + '.id'), primary_key =
> > True)
> >    out = {'__tablename__': name,
> >           'id': id_,
> >           '__mapper_args__': {'polymorphic_identity': name,
> > 'inherit_condition': (id_ == classes[basename].id)}}
>
> > But I am getting a (maybe unrelated) error. Should this solution work?
>
> that approach seems fine though classes[basename] must be already 
> established, I might pull it just from the superclass that you're passing 
> into type().

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[sqlalchemy] Re: order of initialization __mapper_args__ 'inherit_condition' and primary key

[lars van gemerden]

OK, thanks, the order wasn't the problem, I am using this for the
initialization of my classes:

dicty= {'__tablename__': name,
   'id': Column(Integer, ForeignKey(basename + '.id'),
primary_key = True),
   '__mapper_args__': {'polymorphic_identity': name,
'inherit_condition': (id == classes[basename].id)}}

and as you said 'id' in the last line refers to the id() function. I
think I fixed it by changing the code to:

id_ = Column(Integer, ForeignKey(basename + '.id'), primary_key =
True)
out = {'__tablename__': name,
   'id': id_,
   '__mapper_args__': {'polymorphic_identity': name,
'inherit_condition': (id_ == classes[basename].id)}}

But I am getting a (maybe unrelated) error. Should this solution work?

Cheers, Lars


On Feb 23, 4:07 pm, Michael Bayer  wrote:
> On Feb 23, 2012, at 9:56 AM, lars van gemerden wrote:
>
>
>
>
>
>
>
>
>
> > Hi all,
>
> > I reproduced an error I was having with the code below (basically
> > pasted from the tutorial for joined inheritance) and added an
> > 'inherit_condition' to __mapper_args__ of the subclass. At that point
> > the code started throwing a sqlalchemy.exc.InterfaceError. The code
> > is:
>
> > class Person(Base):
> >    __tablename__ = 'Person'
> >    id = Column(Integer, primary_key=True)
> >    discriminator = Column('type', String(50))
> >    __mapper_args__ = {'polymorphic_on': discriminator}
>
> > class Engineer(Person):
> >    __tablename__ = 'Engineer'
> >    __mapper_args__ = {'polymorphic_identity': 'Engineer',
> > 'inherit_condition': (id == Person.id)}
> >    id = Column(Integer, ForeignKey('Person.id'), primary_key=True)
>
> Well OK, right here, when you say "id", that's the Python built-in function 
> "id()".   This because the name "id" has not yet been assigned to point to 
> your new Column object.   The "class Engineer(Person):" is just another 
> Python block, just like an "if :" statement.   So yes, in that 
> case you need to ensure "id" is pointing to that Column before you stick it 
> into the "inherit_condition".    This has nothing to do with the order of 
> things being looked at in the actual "dict" of the class, just the order of 
> how Python is assigning meaning to the name "id" within the "class:" block.
>
> The declarative tutorial doesn't have this bug, but yes I can see we might be 
> better off illustrating __mapper_args__ at the bottom of the class 
> declaration just to make this kind of error less likely.
>
>
>
> > Now we get to the problem: In my code I dynamically generate tables
> > with type(name, (base,), dicty). In dicty are the __mapper_args__  and
> > id Column. Because of the dictionary used I have no control over the
> > order of the arguments and that seems to cause my exception.
>
> I'm not getting how you'd have this issue there - you of course have total 
> control over what goes into a dict() to use with type(), and in what order 
> (it's only on the "taking things out" part of a dict that is not ordered).  
> You should generate the Column object, then you put it in the dictionary.   
> The "id" builtin function never gets involved:
>
> id = Column(...)
> dict = {
>     'id':id,
>    '__mapper_args__':{'inherit_condition':id==Person.id}
>
>
>
>
>
>
>
> }

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[sqlalchemy] order of initialization __mapper_args__ 'inherit_condition' and primary key

[lars van gemerden]

Hi all,

I reproduced an error I was having with the code below (basically
pasted from the tutorial for joined inheritance) and added an
'inherit_condition' to __mapper_args__ of the subclass. At that point
the code started throwing a sqlalchemy.exc.InterfaceError. The code
is:

-

from sqlalchemy import *
from sqlalchemy.orm.session import sessionmaker
from sqlalchemy.ext.declarative import declarative_base

engine = create_engine('sqlite:///:memory:', echo=False)
Base = declarative_base(bind = engine)
Session = sessionmaker(bind = engine)


def setup(engine):
Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine)
return Session()

class Person(Base):
__tablename__ = 'Person'
id = Column(Integer, primary_key=True)
discriminator = Column('type', String(50))
__mapper_args__ = {'polymorphic_on': discriminator}


class Engineer(Person):
__tablename__ = 'Engineer'
__mapper_args__ = {'polymorphic_identity': 'Engineer',
'inherit_condition': (id == Person.id)}
id = Column(Integer, ForeignKey('Person.id'), primary_key=True)

if __name__ == '__main__':
session = setup(engine)
e = Engineer()
session.add_all([e])
session.commit()
print e.discriminator

and the error:


Traceback (most recent call last):
  File "D:\Documents\Code\Eclipse\workspace\SQLAdata\src\test5.py",
line 38, in 
print e.discriminator
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\attributes.py",
line 168, in __get__
return self.impl.get(instance_state(instance),dict_)
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\attributes.py",
line 451, in get
value = callable_(passive)
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\state.py", line
285, in __call__
self.manager.deferred_scalar_loader(self, toload)
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line
1701, in _load_scalar_attributes
only_load_props=attribute_names)
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\query.py", line
2378, in _load_on_ident
return q.one()
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\query.py", line
2050, in one
ret = list(self)
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\query.py", line
2093, in __iter__
return self._execute_and_instances(context)
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\query.py", line
2108, in _execute_and_instances
result = conn.execute(querycontext.statement, self._params)
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\base.py", line
1405, in execute
params)
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\base.py", line
1538, in _execute_clauseelement
compiled_sql, distilled_params
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\base.py", line
1646, in _execute_context
context)
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\base.py", line
1639, in _execute_context
context)
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\default.py",
line 330, in do_execute
cursor.execute(statement, parameters)
sqlalchemy.exc.InterfaceError: (InterfaceError) Error binding
parameter 0 - probably unsupported type. u'SELECT "Person".type AS
"Person_type", "Engineer".id AS "Engineer_id", "Person".id AS
"Person_id" \nFROM "Person" JOIN "Engineer" ON "Person".id = ? \nWHERE
"Person".id = ?' (, 1)
-
I fixed the error by moving the id Column in Engineer above the
__mapper_args__ :

-
class Engineer(Person):
__tablename__ = 'Engineer'
id = Column(Integer, ForeignKey('Person.id'), primary_key=True)
__mapper_args__ = {'polymorphic_identity': 'Engineer',
'inherit_condition': (id == Person.id)}
-

Now we get to the problem: In my code I dynamically generate tables
with type(name, (base,), dicty). In dicty are the __mapper_args__  and
id Column. Because of the dictionary used I have no control over the
order of the arguments and that seems to cause my exception. If I add
the __mapper_args__  with 'inherit_condition' to the class later, I
get another exception (ArgumentError: Can't determine join between
'person' and 'child'; tables have more than one foreign key constraint
relationship between them. Please specify the 'onclause' of this join
explicitly.)

Could the order in 'dicty' be the problem? Can anyone help me with a
solution or workaround for this problem.

Cheers, Lars

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[sqlalchemy] Re: problem with dynamic tables/classes and inheritance

[lars van gemerden]

Seems a finally got what I wanted to achieve. Changed a lot of things,
so I cannot pinpoint the error(s) in the code above. If anyone is
interested I will help/share the solution I found.

Cheers, Lars

On Feb 22, 8:35 pm, lars van gemerden  wrote:
> I am trying to generate tables/classes dynamically. The code below is
> my latest attempt, but I cannot get it to work.
>
> -
>  class TableName(object):
>     @declared_attr
>     def __tablename__(cls): return cls.__name__
>
> class Inherit(object):
>     @declared_attr
>     def id(cls): #<= is not called for S
>         base = cls.__bases__[len(cls.__bases__) - 1]
>         print "class, base:", cls.__name__, base.__name__
>         return Column(Integer, ForeignKey(base.__name__ + '.id'),
> primary_key = True)
>     @declared_attr
>     def __mapper_args__(cls):
>         return {'polymorphic_identity': cls.__name__}
>
> class Object(Base, TableName):
>
>     association_tables = {}
>
>     id = Column(Integer, primary_key = True)
>     type_name = Column(String(50),  nullable = False)
>     __mapper_args__ = {'polymorphic_on': type_name}
>
> if __name__ == '__main__':
>     session = setup(engine)
>
>     T = type('T', (Inherit, Object), {'Tdata': Column(String(50))})
>     S = type('S', (T,), {'Sdata': Column(String(50))}) #<= Error
>     session.commit()
>     print S.__table__.c
> -
> the output is:
> -
> class, base: T Object
> class, base: T Object
> class, base: T Object
> Traceback (most recent call last):
>   File "D:\Documents\Code\Eclipse\workspace\SQLAdata\src\test4.py",
> line 55, in 
>     S = type('S', (T,), {'Sdata': Column(String(50))})
>   File "C:\Python27\lib\site-packages\sqlalchemy\ext\declarative.py",
> line 1336, in __init__
>     _as_declarative(cls, classname, cls.__dict__)
>   File "C:\Python27\lib\site-packages\sqlalchemy\ext\declarative.py",
> line 1329, in _as_declarative
>     **mapper_args)
>   File "C:\Python27\lib\site-packages\sqlalchemy\orm\__init__.py",
> line 1116, in mapper
>     return Mapper(class_, local_table, *args, **params)
>   File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line
> 197, in __init__
>     self._configure_inheritance()
>   File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line
> 473, in _configure_inheritance
>     self.local_table)
>   File "C:\Python27\lib\site-packages\sqlalchemy\sql\util.py", line
> 303, in join_condition
>     "between '%s' and '%s'.%s" % (a.description, b.description, hint))
> sqlalchemy.exc.ArgumentError: Can't find any foreign key relationships
> between 'T' and 'S'.
> -
> What is wrong with this approach. Is there a good way to approach this
> problem (I have tried a couple already).
>
> Also: Why is Inherit.id() called 3 times for T
>
> Please help!
>
> Lars

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[sqlalchemy] problem with dynamic tables/classes and inheritance

[lars van gemerden]

I am trying to generate tables/classes dynamically. The code below is
my latest attempt, but I cannot get it to work.

-
 class TableName(object):
@declared_attr
def __tablename__(cls): return cls.__name__

class Inherit(object):
@declared_attr
def id(cls): #<= is not called for S
base = cls.__bases__[len(cls.__bases__) - 1]
print "class, base:", cls.__name__, base.__name__
return Column(Integer, ForeignKey(base.__name__ + '.id'),
primary_key = True)
@declared_attr
def __mapper_args__(cls):
return {'polymorphic_identity': cls.__name__}

class Object(Base, TableName):

association_tables = {}

id = Column(Integer, primary_key = True)
type_name = Column(String(50),  nullable = False)
__mapper_args__ = {'polymorphic_on': type_name}



if __name__ == '__main__':
session = setup(engine)

T = type('T', (Inherit, Object), {'Tdata': Column(String(50))})
S = type('S', (T,), {'Sdata': Column(String(50))}) #<= Error
session.commit()
print S.__table__.c
-
the output is:
-
class, base: T Object
class, base: T Object
class, base: T Object
Traceback (most recent call last):
  File "D:\Documents\Code\Eclipse\workspace\SQLAdata\src\test4.py",
line 55, in 
S = type('S', (T,), {'Sdata': Column(String(50))})
  File "C:\Python27\lib\site-packages\sqlalchemy\ext\declarative.py",
line 1336, in __init__
_as_declarative(cls, classname, cls.__dict__)
  File "C:\Python27\lib\site-packages\sqlalchemy\ext\declarative.py",
line 1329, in _as_declarative
**mapper_args)
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\__init__.py",
line 1116, in mapper
return Mapper(class_, local_table, *args, **params)
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line
197, in __init__
self._configure_inheritance()
  File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line
473, in _configure_inheritance
self.local_table)
  File "C:\Python27\lib\site-packages\sqlalchemy\sql\util.py", line
303, in join_condition
"between '%s' and '%s'.%s" % (a.description, b.description, hint))
sqlalchemy.exc.ArgumentError: Can't find any foreign key relationships
between 'T' and 'S'.
-
What is wrong with this approach. Is there a good way to approach this
problem (I have tried a couple already).

Also: Why is Inherit.id() called 3 times for T

Please help!

Lars

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[sqlalchemy] @validates & clean-up

[lars van gemerden]

I am having some trouble cleaning up after my @validates method throws
an exception. The validation is of a relationship attribute and the
foreign record should be removed. Are there some general tips?
Otherwise I will post a code example.

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[sqlalchemy] Re: Elixir question

[lars van gemerden]

Sorry, scrap the remark about primaryjoin ... inheritance. INheritance
wasn't the problem.

On Feb 5, 1:27 pm, lars van gemerden  wrote:
> OK, thank you,
>
> I went back to SQLA and came up with this for now (simplified):
> 
> class Pairs(Base):
>     __tablename__ = 'Pairs'
>     name = Column(String(20), primary_key=True)
>     other_name = Column(String(20), ForeignKey('Pairs.name'), nullable
> = False)
>
>     other = relationship('Pairs',
>                           primaryjoin = 'Pairs.name ==
> Pairs.other_name',
>                           remote_side=[name])
>     def __init__(self, name):
>         self.name = name
>     def __repr__(self):
>         return "(%s, %s)" % (self.name, self.other.name)
>
> def pair(name1, name2):
>     p1, p2 = Pairs(name1), Pairs(name2)
>     p1.other_name = name2
>     p2.other_name = name1
>     return p1, p2
>
> if __name__ == '__main__':
>
>     p1, p2 = pair('apple', 'pear')
>     session.add_all([p1, p2])
>     session.commit()
>     for p in session.query(Pairs).all():
>         print p
>     assert p1.other.other is p1
> --
> Note that there is no backref on "other" and that the primaryjoin is
> completely written out (otherwise a got a mysterious (to me) error,
> when using joined inheritance at the same time).
>
> This solution is key to my datamodel. Does anyone see any drawbacks?
>
> Cheers, Lars
>
> On Feb 5, 10:50 am, Gaëtan de Menten  wrote:
>
>
>
>
>
>
>
> > On 02/03/2012 12:08 PM, lars van gemerden wrote:
>
> > > I should probably make the pair method:
>
> > > def pair(name1, name2):
> > >      p1, p2 = Pairs(name1), Pairs(name2)
> > >      p1.other = p2
> > >      p2.other = p1
>
> > > On Feb 3, 11:57 am, lars van gemerden  wrote:
> > >> Hi, I am trying to sote pairs in a table as follows:
>
> > >> #--
> > >>  
> > >> from elixir import *
>
> > >> metadata.bind = "sqlite:///:memory:"
> > >> metadata.bind.echo = False
>
> > >> class Pairs(Entity):
> > >>      name = Field(String(50), primary_key = True)
> > >>      other = OneToOne('Pairs', inverse = 'other')
>
> > You can't have a OneToOne as inverse for a OneToOne, even less for
> > itself. Valid relationship pairs are:
>
> > ManyToOne - OneToOne
> > ManyToOne - OneToMany
> > ManyToMany - ManyToMany
>
> > In your case you want:
>
> > class Pairs(Entity):
> >      name = Field(String(50), primary_key = True)
> >      other1 = ManyToOne('Pairs', inverse = 'other2')
> >      other2 = OneToOne('Pairs', inverse = 'other1')
>
> > and if your database really only stores pairs, a property might make it
> > more elegant:
>
> >      @property
> >      def other(self):
> >          return self.other1 if self.other1 is not None else self.other2
>
> > As a side note, you probably do not want to use Elixir for a new
> > project, as Elixir is not maintained anymore.
>
> > -G.

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[sqlalchemy] Re: Elixir question

[lars van gemerden]

OK, thank you,

I went back to SQLA and came up with this for now (simplified):

class Pairs(Base):
__tablename__ = 'Pairs'
name = Column(String(20), primary_key=True)
other_name = Column(String(20), ForeignKey('Pairs.name'), nullable
= False)

other = relationship('Pairs',
  primaryjoin = 'Pairs.name ==
Pairs.other_name',
  remote_side=[name])
def __init__(self, name):
self.name = name
def __repr__(self):
return "(%s, %s)" % (self.name, self.other.name)

def pair(name1, name2):
p1, p2 = Pairs(name1), Pairs(name2)
p1.other_name = name2
p2.other_name = name1
return p1, p2

if __name__ == '__main__':

p1, p2 = pair('apple', 'pear')
session.add_all([p1, p2])
session.commit()
for p in session.query(Pairs).all():
print p
assert p1.other.other is p1
--
Note that there is no backref on "other" and that the primaryjoin is
completely written out (otherwise a got a mysterious (to me) error,
when using joined inheritance at the same time).

This solution is key to my datamodel. Does anyone see any drawbacks?

Cheers, Lars




On Feb 5, 10:50 am, Gaëtan de Menten  wrote:
> On 02/03/2012 12:08 PM, lars van gemerden wrote:
>
>
>
>
>
>
>
> > I should probably make the pair method:
>
> > def pair(name1, name2):
> >      p1, p2 = Pairs(name1), Pairs(name2)
> >      p1.other = p2
> >      p2.other = p1
>
> > On Feb 3, 11:57 am, lars van gemerden  wrote:
> >> Hi, I am trying to sote pairs in a table as follows:
>
> >> #--
> >>  
> >> from elixir import *
>
> >> metadata.bind = "sqlite:///:memory:"
> >> metadata.bind.echo = False
>
> >> class Pairs(Entity):
> >>      name = Field(String(50), primary_key = True)
> >>      other = OneToOne('Pairs', inverse = 'other')
>
> You can't have a OneToOne as inverse for a OneToOne, even less for
> itself. Valid relationship pairs are:
>
> ManyToOne - OneToOne
> ManyToOne - OneToMany
> ManyToMany - ManyToMany
>
> In your case you want:
>
> class Pairs(Entity):
>      name = Field(String(50), primary_key = True)
>      other1 = ManyToOne('Pairs', inverse = 'other2')
>      other2 = OneToOne('Pairs', inverse = 'other1')
>
> and if your database really only stores pairs, a property might make it
> more elegant:
>
>      @property
>      def other(self):
>          return self.other1 if self.other1 is not None else self.other2
>
> As a side note, you probably do not want to use Elixir for a new
> project, as Elixir is not maintained anymore.
>
> -G.

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[sqlalchemy] Re: a more general elixir question

[lars van gemerden]

Too bad, thanks

On Feb 3, 1:38 pm, erikj  wrote:
> no, that's not possible
>
> Elixir does some custom postprocessing on a class
> definition, and so does Declarative, but they are not
> interoperatable
>
> On Feb 3, 1:20 pm, lars van gemerden  wrote:
>
>
>
>
>
>
>
> > Thanks,
>
> > Can you also mix Elixir Fields and SQLA Column/relationships in the
> > same class?
>
> > Cheers, Lars
>
> > On Feb 3, 12:56 pm, erikj  wrote:
>
> > > yes
>
> > > Elixir classes are in fact SQLA classes, only defined with
> > > a different syntax
>
> > > you can mix Elixir, Declarative and plain python objects mapped
> > > with SQLA
>
> > > On Feb 3, 12:13 pm, lars van gemerden  wrote:
>
> > > > Is it possible to mix Elixir classes and SQLA classes in one database
> > > > (with foreign keys between them)?
>
> > > > Cheers, Lars

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[sqlalchemy] Re: a more general elixir question

[lars van gemerden]

Thanks,

Can you also mix Elixir Fields and SQLA Column/relationships in the
same class?

Cheers, Lars

On Feb 3, 12:56 pm, erikj  wrote:
> yes
>
> Elixir classes are in fact SQLA classes, only defined with
> a different syntax
>
> you can mix Elixir, Declarative and plain python objects mapped
> with SQLA
>
> On Feb 3, 12:13 pm, lars van gemerden  wrote:
>
>
>
>
>
>
>
> > Is it possible to mix Elixir classes and SQLA classes in one database
> > (with foreign keys between them)?
>
> > Cheers, Lars

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[sqlalchemy] a more general elixir question

[lars van gemerden]

Is it possible to mix Elixir classes and SQLA classes in one database
(with foreign keys between them)?

Cheers, Lars

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[sqlalchemy] Re: Elixir question

[lars van gemerden]

I should probably make the pair method:

def pair(name1, name2):
p1, p2 = Pairs(name1), Pairs(name2)
p1.other = p2
p2.other = p1

On Feb 3, 11:57 am, lars van gemerden  wrote:
> Hi, I am trying to sote pairs in a table as follows:
>
> #-- 
> 
> from elixir import *
>
> metadata.bind = "sqlite:///:memory:"
> metadata.bind.echo = False
>
> class Pairs(Entity):
>     name = Field(String(50), primary_key = True)
>     other = OneToOne('Pairs', inverse = 'other')
>
>     def __init__(self, name):
>         self.name = name
>
> def pair(name1, name2):
>     p1, p2 = Pairs(name1), Pairs(name2)
>     p1.other = p2
>
> if __name__ == '__main__':
>
>     setup_all()
>     create_all()
>
>     pair('p1', 'p2')
> #-- 
> 
>
> I am not very famiiar with SQL etc. but logically this seems possible
> (please orrect me if I am wrong). However I get the following error:
> 
> File "D:\Documents\Code\Eclipse\workspace\SQLAdata\src\tests.py", line
> 22, in 
>     setup_all()
>   File "build\bdist.win-amd64\egg\elixir\__init__.py", line 94, in
> setup_all
>
>   File "build\bdist.win-amd64\egg\elixir\entity.py", line 951, in
> setup_entities
>   File "build\bdist.win-amd64\egg\elixir\entity.py", line 198, in
> create_pk_cols
>   File "build\bdist.win-amd64\egg\elixir\entity.py", line 481, in
> call_builders
>   File "build\bdist.win-amd64\egg\elixir\relationships.py", line 448,
> in create_pk_cols
>   File "build\bdist.win-amd64\egg\elixir\relationships.py", line 791,
> in create_keys
>   File "build\bdist.win-amd64\egg\elixir\relationships.py", line 521,
> in inverse
> AssertionError: Relationships 'other' in entity 'Pair' and 'other' in
> entity 'Pair' cannot be inverse of each other because their types do
> not form a valid combination.
> 
>
> Can anyone help me to understand the error and possibly fix it?
>
> Thanks in advance, Lars

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