Re: [sqlalchemy] Declarative syntax with column_property (v0.6.3)
Hi Michael,
I'm guilty of two over-simplifications in the code used in my example...
Firstly, the substring property/column (with which I had a problem) applies
to a subclass (using joined table inheritance) and the variable to which
it applies is specified in its parent class. Hence, I started by assuming
that I'd need something along the lines of:
class Parent(Base):
my_string
class Child(Parent):
@classproperty/@property/ some other decorator
def my_substr(cls):
return column_property ( cls.my_string )
However, trying this (ie the classproperty/column_property within Child),
returned sqlalchemy.orm.properties.ColumnProperty object ... (the error
I referred to in my original question)
I'm confused about why I'm not able to get this (or some variation of it) to
work. Is this indeed possible?
Looking at the documentation (as a consequence of the error), my I was drawn
to the syntax used in the section on 'mixins' (ie, the column_property
defined externally).
My second over-simplification regards the the function itself. The function
I'm trying to use [which I'm aware doesn't translate easily to sqlite], is:
func.substr(cls.my_str, func.instr(cls.my_str, )+1, 2)
Now, thanks to your response, I now actually have the following *working*
(using mysql):
class MySubStr(object):
@classproperty
def my_substr(cls):
return column_property(
func.substr(cls.my_string, func.instr(cls.my_string,
)+1, 2)
)
However, replacing:
func.substr(cls.my_string, func.instr(cls.my_string, )+1, 2)
with (in order to attach a label to the column):
select([func.substr(cls.my_string, func.instr(cls.my_string, )+1,
2)]).label('exch_code')
Gives me -- AttributeError: 'NoneType' object has no attribute '_keymap'
(full traceback below).
Apologies for my earlier over-simplification (and my late response!). And I
hope that what I've responded with is clear!!
Regards,
Rob
-
/home/robertsudwarts/tg2env/lib/python2.6/site-packages/SQLAlchemy-0.6.3-py2.6.egg/sqlalchemy/orm/query.pyc
in one(self)
1520
1521
- 1522 ret = list(self)
1523
1524 l = len(ret)
/home/robertsudwarts/tg2env/lib/python2.6/site-packages/SQLAlchemy-0.6.3-py2.6.egg/sqlalchemy/orm/query.pyc
in instances(self, cursor, _Query__context)
1667 break
1668 else:
- 1669 fetch = cursor.fetchall()
1670
1671 if custom_rows:
/home/robertsudwarts/tg2env/lib/python2.6/site-packages/SQLAlchemy-0.6.3-py2.6.egg/sqlalchemy/engine/base.pyc
in fetchall(self)
2381
2382 try:
- 2383 l = self.process_rows(self._fetchall_impl())
2384 self.close()
2385 return l
/home/robertsudwarts/tg2env/lib/python2.6/site-packages/SQLAlchemy-0.6.3-py2.6.egg/sqlalchemy/engine/base.pyc
in process_rows(self, rows)
2364 process_row = self._process_row
2365 metadata = self._metadata
- 2366 keymap = metadata._keymap
2367 processors = metadata._processors
2368 if self._echo:
AttributeError: 'NoneType' object has no attribute '_keymap'
On 2 August 2010 19:42, Michael Bayer mike...@zzzcomputing.com wrote:
On Aug 2, 2010, at 1:40 PM, Michael Bayer wrote:
On Aug 2, 2010, at 12:19 PM, Robert Sudwarts wrote:
Hi,
I'm having trouble understanding the correct syntax to be used with
Declarative and a column property.
The select statement I'm using is:
select([func.substr(my_table.c.my_string, 2, 3)]).label(my_substr'),
deferred=True
And (as per the docs using the expanded syntax, this works as expected.
With the Declarative syntax, I've tried:
from sqlalchemy.util import classproperty
from sqlalchemy.orm..., column_property
class MySubstr(object):
@classproperty
def my_substr(cls):
return column_property(
select([func.substr(cls.my_str, 2, 3)]).label('my_substr')
)
class MyTable(Base, MySubstr):
.
and then expect to be able to call a record in MyTable and return its
my_substr, however, all I'm getting is a representation of the object ...
eg sqlalchemy.orm.properties.ColumnProperty object at 0xa4951cc and
no apparent way of seeing its value.
oh and also, you don't need the select() here either:
class MyTable(Base):
__tablename__ = 'foo'
id = Column(Integer, primary_key=True)
my_str = Column('my_str', String)
my_substr = column_property(func.substr(cls.my_str, 2, 3))
I see nothing wrong with the example, the only potential glitch is that
my_str needs to have a name assigned up front. You didn't illustrate that
part here, so FYI it would be extremely
Re: [sqlalchemy] Declarative syntax with column_property (v0.6.3)
On Aug 3, 2010, at 7:47 AM, Robert Sudwarts wrote:
Hi Michael,
I'm guilty of two over-simplifications in the code used in my example...
Firstly, the substring property/column (with which I had a problem) applies
to a subclass (using joined table inheritance) and the variable to which it
applies is specified in its parent class. Hence, I started by assuming that
I'd need something along the lines of:
class Parent(Base):
my_string
class Child(Parent):
@classproperty/@property/ some other decorator
def my_substr(cls):
return column_property ( cls.my_string )
However, trying this (ie the classproperty/column_property within Child),
returned sqlalchemy.orm.properties.ColumnProperty object ... (the error I
referred to in my original question)
I'm confused about why I'm not able to get this (or some variation of it) to
work. Is this indeed possible?
Just yesterday, in response to this, I added a line of code such that if you
specifically use @classproperty on the declarative class (i.e. not a mixin),
declarative will call it to figure out what it returns and configure it
normally- previously, if the attribute were not directly a MapperProperty, it
would be ignored.However, I couldn't think of any use case that this is
actually useful for. I thought that, it might be a way to establish a
column-oriented property late, so that you could get around imports not being
available. At the moment, it's not useful for that, because declarative calls
the attribute as soon as the class is created, and whatever imports that werent
available to the class declaration are still not present.
So what are you gaining above, if it were working in 0.6.3, by using
@classproperty instaed of my_substr = column_property() ? Anywhere you
reference cls in your function, you'd just reference whatever is local, or
part of Parent.
Looking at the documentation (as a consequence of the error), my I was drawn
to the syntax used in the section on 'mixins' (ie, the column_property
defined externally).
My second over-simplification regards the the function itself. The function
I'm trying to use [which I'm aware doesn't translate easily to sqlite], is:
func.substr(cls.my_str, func.instr(cls.my_str, )+1, 2)
Now, thanks to your response, I now actually have the following *working*
(using mysql):
class MySubStr(object):
@classproperty
def my_substr(cls):
return column_property(
func.substr(cls.my_string,
func.instr(cls.my_string, )+1, 2)
)
However, replacing:
func.substr(cls.my_string, func.instr(cls.my_string, )+1, 2)
with (in order to attach a label to the column):
select([func.substr(cls.my_string, func.instr(cls.my_string, )+1,
2)]).label('exch_code')
Gives me -- AttributeError: 'NoneType' object has no attribute '_keymap'
(full traceback below).
That's a really weird error. It suggests that the result is not one that
returns any rows, not like its a SELECT with zero rows, rather, it is perceived
by SQLite as something like an INSERT that isn't meant to return any rows, and
there's no cursor.description. The ResultProxy is then failing ungracefully
which is surprising (looking at the current source it appears we need to cover
this situation). It would be interesting to try out the raw SQL to see what
is produced, since the statement is definitely a SELECT - pysqlite should raise
an error if it doesn't like the SQL, or give us a cursor.description.
Anyway, your column_property() doesn't need the select() here, you can just
call .label() on the func.substr() result, but also, you don't really need the
label() in here either (unless I'm missing something? )
Apologies for my earlier over-simplification (and my late response!). And I
hope that what I've responded with is clear!!
Regards,
Rob
-
/home/robertsudwarts/tg2env/lib/python2.6/site-packages/SQLAlchemy-0.6.3-py2.6.egg/sqlalchemy/orm/query.pyc
in one(self)
1520
1521
- 1522 ret = list(self)
1523
1524 l = len(ret)
/home/robertsudwarts/tg2env/lib/python2.6/site-packages/SQLAlchemy-0.6.3-py2.6.egg/sqlalchemy/orm/query.pyc
in instances(self, cursor, _Query__context)
1667 break
1668 else:
- 1669 fetch = cursor.fetchall()
1670
1671 if custom_rows:
/home/robertsudwarts/tg2env/lib/python2.6/site-packages/SQLAlchemy-0.6.3-py2.6.egg/sqlalchemy/engine/base.pyc
in fetchall(self)
2381
2382 try:
- 2383 l = self.process_rows(self._fetchall_impl())
2384 self.close()
2385 return l
Re: [sqlalchemy] Declarative syntax with column_property (v0.6.3)
Please see my comments below.
Regards,
Rob
On 3 August 2010 14:05, Michael Bayer mike...@zzzcomputing.com wrote:
On Aug 3, 2010, at 7:47 AM, Robert Sudwarts wrote:
Hi Michael,
I'm guilty of two over-simplifications in the code used in my example...
Firstly, the substring property/column (with which I had a problem) applies
to a subclass (using joined table inheritance) and the variable to which
it applies is specified in its parent class. Hence, I started by assuming
that I'd need something along the lines of:
class Parent(Base):
my_string
class Child(Parent):
@classproperty/@property/ some other decorator
def my_substr(cls):
return column_property ( cls.my_string )
However, trying this (ie the classproperty/column_property within Child),
returned sqlalchemy.orm.properties.ColumnProperty object ... (the error
I referred to in my original question)
I'm confused about why I'm not able to get this (or some variation of it)
to work. Is this indeed possible?
Just yesterday, in response to this, I added a line of code such that if
you specifically use @classproperty on the declarative class (i.e. not a
mixin), declarative will call it to figure out what it returns and configure
it normally- previously, if the attribute were not directly a
MapperProperty, it would be ignored.However, I couldn't think of any use
case that this is actually useful for. I thought that, it might be a way to
establish a column-oriented property late, so that you could get around
imports not being available. At the moment, it's not useful for that,
because declarative calls the attribute as soon as the class is created, and
whatever imports that werent available to the class declaration are still
not present.
Ah! Right!! I hadn't understood that ... I assumed (wrongly) that I'd have
to 'instantitate' 'cls' somehow using a decorator+function: def blah(cls):
...
I didn't realise that I could simply use Parent.my_str
So what are you gaining above, if it were working in 0.6.3, by using
@classproperty instaed of my_substr = column_property() ? Anywhere you
reference cls in your function, you'd just reference whatever is local, or
part of Parent.
Looking at the documentation (as a consequence of the error), my I was
drawn to the syntax used in the section on 'mixins' (ie, the column_property
defined externally).
My second over-simplification regards the the function itself. The
function I'm trying to use [which I'm aware doesn't translate easily to
sqlite], is:
func.substr(cls.my_str, func.instr(cls.my_str, )+1, 2)
Now, thanks to your response, I now actually have the following *working*
(using mysql):
class MySubStr(object):
@classproperty
def my_substr(cls):
return column_property(
func.substr(cls.my_string,
func.instr(cls.my_string, )+1, 2)
)
However, replacing:
func.substr(cls.my_string, func.instr(cls.my_string, )+1, 2)
with (in order to attach a label to the column):
select([func.substr(cls.my_string, func.instr(cls.my_string, )+1,
2)]).label('exch_code')
Gives me -- AttributeError: 'NoneType' object has no attribute '_keymap'
(full traceback below).
That's a really weird error. It suggests that the result is not one that
returns any rows, not like its a SELECT with zero rows, rather, it is
perceived by SQLite as something like an INSERT that isn't meant to return
any rows, and there's no cursor.description. The ResultProxy is then
failing ungracefully which is surprising (looking at the current source it
appears we need to cover this situation). It would be interesting to try
out the raw SQL to see what is produced, since the statement is definitely a
SELECT - pysqlite should raise an error if it doesn't like the SQL, or give
us a cursor.description.
Just to be clear -- this error/traceback was produced with MySQL as the
database
Anyway, your column_property() doesn't need the select() here, you can just
call .label() on the func.substr() result, but also, you don't really need
the label() in here either (unless I'm missing something? )
Again ... I hadn't realised that I could apply .label() to the directly to
'func' ... I've changed this and it works.
Apologies for my earlier over-simplification (and my late response!). And
I hope that what I've responded with is clear!!
Regards,
Rob
-
/home/robertsudwarts/tg2env/lib/python2.6/site-packages/SQLAlchemy-0.6.3-py2.6.egg/sqlalchemy/orm/query.pyc
in one(self)
1520
1521
- 1522 ret = list(self)
1523
1524 l = len(ret)
/home/robertsudwarts/tg2env/lib/python2.6/site-packages/SQLAlchemy-0.6.3-py2.6.egg/sqlalchemy/orm/query.pyc
in instances(self, cursor, _Query__context)
[sqlalchemy] Declarative syntax with column_property (v0.6.3)
Hi,
I'm having trouble understanding the correct syntax to be used with
Declarative and a column property.
The select statement I'm using is:
select([func.substr(my_table.c.my_string, 2, 3)]).label(my_substr'),
deferred=True
And (as per the docs using the expanded syntax, this works as expected.
With the Declarative syntax, I've tried:
from sqlalchemy.util import classproperty
from sqlalchemy.orm..., column_property
class MySubstr(object):
@classproperty
def my_substr(cls):
return column_property(
select([func.substr(cls.my_str, 2, 3)]).label('my_substr')
)
class MyTable(Base, MySubstr):
.
and then expect to be able to call a record in MyTable and return its
my_substr, however, all I'm getting is a representation of the object ...
eg sqlalchemy.orm.properties.ColumnProperty object at 0xa4951cc and no
apparent way of seeing its value.
Should the @classproperty sit within the MyTable(Base) itself (ie is there
a need for the separate object -- and have I been confused by the section on
'mixins' )?
I'd be really grateful for any clues!
Many thanks,
Rob
--
You received this message because you are subscribed to the Google Groups
sqlalchemy group.
To post to this group, send email to sqlalch...@googlegroups.com.
To unsubscribe from this group, send email to
sqlalchemy+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en.
Re: [sqlalchemy] Declarative syntax with column_property (v0.6.3)
On Aug 2, 2010, at 12:19 PM, Robert Sudwarts wrote:
Hi,
I'm having trouble understanding the correct syntax to be used with
Declarative and a column property.
The select statement I'm using is: select([func.substr(my_table.c.my_string,
2, 3)]).label(my_substr'), deferred=True
And (as per the docs using the expanded syntax, this works as expected.
With the Declarative syntax, I've tried:
from sqlalchemy.util import classproperty
from sqlalchemy.orm..., column_property
class MySubstr(object):
@classproperty
def my_substr(cls):
return column_property(
select([func.substr(cls.my_str, 2, 3)]).label('my_substr')
)
class MyTable(Base, MySubstr):
.
and then expect to be able to call a record in MyTable and return its
my_substr, however, all I'm getting is a representation of the object ...
eg sqlalchemy.orm.properties.ColumnProperty object at 0xa4951cc and no
apparent way of seeing its value.
I see nothing wrong with the example, the only potential glitch is that
my_str needs to have a name assigned up front. You didn't illustrate that
part here, so FYI it would be extremely helpful if you could attach fully
working examples. In this case the example is:
from sqlalchemy import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.util import classproperty
from sqlalchemy.orm import column_property, sessionmaker
Base = declarative_base()
engine = create_engine('sqlite://', echo=True)
class MySubstr(object):
@classproperty
def my_substr(cls):
return column_property(
select([func.substr(cls.my_str, 2,
3)]).label('my_substr')
)
class MyTable(Base, MySubstr):
__tablename__ = 'foo'
id = Column(Integer, primary_key=True)
my_str = Column('my_str', String)
Base.metadata.create_all(engine)
sess = sessionmaker(engine)()
m1 = MyTable(my_str='some string')
sess.add(m1)
sess.commit()
print m1.my_substr
and it works fine.
Should the @classproperty sit within the MyTable(Base) itself (ie is there
a need for the separate object --
@classproperty is typically specific to the mixin use case, which is why its
only discussed in the mixins section of the declarative documentation. It's
a useful construct in other situations but you certainly don't need it if you
aren't using mixins.
and have I been confused by the section on 'mixins' )?
I'm not sure why you're choosing to use a mixin here, as your column_property
appears to be pretty specific to the MyTable class. if the documentation led
you to believe that you needed one, I am extremely curious why that is the case
as mixins are absolutely optional and that would be a serious documentation
bug. Without the mixin, it is:
class MyTable(Base):
__tablename__ = 'foo'
id = Column(Integer, primary_key=True)
my_str = Column('my_str', String)
my_substr = column_property(
select([func.substr(my_str, 2,
3)]).label('my_substr')
)
--
You received this message because you are subscribed to the Google Groups
sqlalchemy group.
To post to this group, send email to sqlalch...@googlegroups.com.
To unsubscribe from this group, send email to
sqlalchemy+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en.
Re: [sqlalchemy] Declarative syntax with column_property (v0.6.3)
On Aug 2, 2010, at 1:40 PM, Michael Bayer wrote:
On Aug 2, 2010, at 12:19 PM, Robert Sudwarts wrote:
Hi,
I'm having trouble understanding the correct syntax to be used with
Declarative and a column property.
The select statement I'm using is:
select([func.substr(my_table.c.my_string, 2, 3)]).label(my_substr'),
deferred=True
And (as per the docs using the expanded syntax, this works as expected.
With the Declarative syntax, I've tried:
from sqlalchemy.util import classproperty
from sqlalchemy.orm..., column_property
class MySubstr(object):
@classproperty
def my_substr(cls):
return column_property(
select([func.substr(cls.my_str, 2, 3)]).label('my_substr')
)
class MyTable(Base, MySubstr):
.
and then expect to be able to call a record in MyTable and return its
my_substr, however, all I'm getting is a representation of the object ...
eg sqlalchemy.orm.properties.ColumnProperty object at 0xa4951cc and no
apparent way of seeing its value.
oh and also, you don't need the select() here either:
class MyTable(Base):
__tablename__ = 'foo'
id = Column(Integer, primary_key=True)
my_str = Column('my_str', String)
my_substr = column_property(func.substr(cls.my_str, 2, 3))
I see nothing wrong with the example, the only potential glitch is that
my_str needs to have a name assigned up front. You didn't illustrate that
part here, so FYI it would be extremely helpful if you could attach fully
working examples. In this case the example is:
from sqlalchemy import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.util import classproperty
from sqlalchemy.orm import column_property, sessionmaker
Base = declarative_base()
engine = create_engine('sqlite://', echo=True)
class MySubstr(object):
@classproperty
def my_substr(cls):
return column_property(
select([func.substr(cls.my_str, 2,
3)]).label('my_substr')
)
class MyTable(Base, MySubstr):
__tablename__ = 'foo'
id = Column(Integer, primary_key=True)
my_str = Column('my_str', String)
Base.metadata.create_all(engine)
sess = sessionmaker(engine)()
m1 = MyTable(my_str='some string')
sess.add(m1)
sess.commit()
print m1.my_substr
and it works fine.
Should the @classproperty sit within the MyTable(Base) itself (ie is there
a need for the separate object --
@classproperty is typically specific to the mixin use case, which is why its
only discussed in the mixins section of the declarative documentation.
It's a useful construct in other situations but you certainly don't need it
if you aren't using mixins.
and have I been confused by the section on 'mixins' )?
I'm not sure why you're choosing to use a mixin here, as your column_property
appears to be pretty specific to the MyTable class. if the documentation
led you to believe that you needed one, I am extremely curious why that is
the case as mixins are absolutely optional and that would be a serious
documentation bug. Without the mixin, it is:
class MyTable(Base):
__tablename__ = 'foo'
id = Column(Integer, primary_key=True)
my_str = Column('my_str', String)
my_substr = column_property(
select([func.substr(my_str, 2,
3)]).label('my_substr')
)
--
You received this message because you are subscribed to the Google Groups
sqlalchemy group.
To post to this group, send email to sqlalch...@googlegroups.com.
To unsubscribe from this group, send email to
sqlalchemy+unsubscr...@googlegroups.com.
For more options, visit this group at
http://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 sqlalch...@googlegroups.com.
To unsubscribe from this group, send email to
sqlalchemy+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en.
