[sqlalchemy] Re: History meta and unique issue
Hi Mike,
Brilliant thanks - that works - spent ages staring at it and missed
the second col.copy()!
Damian
On Oct 17, 6:27 pm, Michael Bayer mike...@zzzcomputing.com wrote:
ah the example has a bug, you're hitting a second part of the code there
where it fetches columns that are placed on a single table child class that
are moved up to the parent. Committing this now, here's a patch:
diff -r 653ae7f17379 examples/versioning/history_meta.py
--- a/examples/versioning/history_meta.py Mon Oct 17 13:14:04 2011 -0400
+++ b/examples/versioning/history_meta.py Mon Oct 17 13:19:41 2011 -0400
@@ -60,6 +60,7 @@
for column in local_mapper.local_table.c:
if column.key not in super_history_mapper.local_table.c:
col = column.copy()
+ col.unique = False
super_history_mapper.local_table.append_column(col)
table = None
this is rd87af238de36
On Oct 17, 2011, at 12:56 PM, Damian wrote:
Hello!
I've run into an odd error whilst using the history meta. I've got a
class which has two sub classes which define some additional columns.
The MainMeter class has a unique constraint on one of the colums.
When I have the history_meta create my history tables, the
trading_point_name column retains its unique constraint despite there
being a col.unique = False in the history meta which should disable
it. I can't quite figure out why this is happening. Any hints would
be appreciated!
class Meter(Base, BaseMixin):
__metaclass__ = VersionedMeta
__tablename__ = meters
id = sa.Column(sa.Integer, primary_key=True)
type = sa.Column(sa.Enum('main_meter', 'check_meter'))
# and so forth
class MainMeter(Meter):
__mapper_args__ = {'polymorphic_identity': 'main_meter'}
trading_point_name = sa.Column(sa.Unicode(255), nullable=True,
unique=True)
#and so forth
class CheckMeter(Meter):
__mapper_args__ = {'polymorphic_identity': 'check_meter'}
#etc
Details:
Sqlalchemy 7.3
Sqlite db backend
Python2.5
Best regards,
Damian
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[sqlalchemy] Deletion
Hi all,
Despite some doc and web digging, I didn't find how to tell sqa to behave
the way I want :
on deletion on Peripheral, also delete in Actuator.
with the following code, the record in Actuator remains after a deletion,
and a subsequent creation fails with IntegrityError.
class Peripheral(Base):
__tablename__ = 'peripheral'
id = Column(Integer, primary_key=True)
label = Column(String(20), nullable=False)
__mapper_args__ = {'polymorphic_on': peripheral_type,
'polymorphic_identity': 'peripheral'}
class Actuator(Peripheral):
__tablename__ = 'actuator'
__mapper_args__ = {'polymorphic_identity': 'actuator'}
id = Column(None, ForeignKey('peripheral.id'), primary_key=True)
duration = Column(Integer)
Any suggestion ?
Regards,
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[sqlalchemy] Cant understand behavior of sqlalchemy while adding same object twice in a session
Hello,
I am working in eclipse IDE.
I have this code in the file :
class User(Base):
__tablename__ = 'users'
id = Column('user_id',Integer,primary_key = True)
name = Column('user_name',String(20))
addresses = relationship(Address)
def __repr__(self):
return User(%s) % self.name
session = Session(bind=engine)
u=User('myname')
session.add(u)
session.flush()
print u.id
I ran this file and it worked fine but then I changed
something.
Now to see the effect I have to run file again and then I
noticed this
Instead of adding two different objects with two different
ids but same name. It simply updated the id of already existing object.
Now I have two questions :
1. What is the reason of this behavior? First of all it should have
made two different objects . But I think it did not do that because it thought
this object is similar to existing one. In that case it should have raised
exception instead of simply my primary key.
2. WHat happened when I ran the file again? It created a brand new
session or continued the previous one?
3. Due to problem mentioned in point no 1. it wasted my early id nos as
when I committed it saved the last one?
I know there is something that I am missing here as I am just a beginner in
sqlalchemy.
Thanks in advance.
Regards,
Manav Goel
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Re: [sqlalchemy] Deletion
How are you doing the delete?
This should delete both.
a = sess.query(Peripheral).filter(Peripheral.label=='some label').one()
sess.delete(a)
sess.commit()
This will not work.
a = sess.query(Peripheral).filter(Peripheral.label=='some
label').delete()
I think the explanation here is that in this case we are creating an
explicit SQL delete statement without adding Peripheral instances to the
session and so there is no knowledge that a related Actuator exists. Someone
else might be able to give a better explanation.
--
Mike Conley
On Tue, Oct 18, 2011 at 9:03 AM, fribes fri...@gmail.com wrote:
Hi all,
Despite some doc and web digging, I didn't find how to tell sqa to behave
the way I want :
on deletion on Peripheral, also delete in Actuator.
with the following code, the record in Actuator remains after a deletion,
and a subsequent creation fails with IntegrityError.
class Peripheral(Base):
__tablename__ = 'peripheral'
id = Column(Integer, primary_key=True)
label = Column(String(20), nullable=False)
__mapper_args__ = {'polymorphic_on': peripheral_type,
'polymorphic_identity': 'peripheral'}
class Actuator(Peripheral):
__tablename__ = 'actuator'
__mapper_args__ = {'polymorphic_identity': 'actuator'}
id = Column(None, ForeignKey('peripheral.id'), primary_key=True)
duration = Column(Integer)
Any suggestion ?
Regards,
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[sqlalchemy] Using collation sequence in SqlAlchemy against Sqlite DB
Could someone help me to set different collation in sqlAlchemy against
Sqlite DB? I tried to execute something like SELECT
icu_load_collation('pl_PL', 'POLISH') when getting a connection but
couldn't
reference the collation sequence when creating the table object, I
keep
getting the following error.
*sqlite3.OperationalError: no such collation sequence: POLISH*
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Re: [sqlalchemy] Deletion
On Oct 18, 2011, at 10:03 AM, fribes wrote:
Hi all,
Despite some doc and web digging, I didn't find how to tell sqa to behave the
way I want :
on deletion on Peripheral, also delete in Actuator.
with the following code, the record in Actuator remains after a deletion, and
a subsequent creation fails with IntegrityError.
class Peripheral(Base):
__tablename__ = 'peripheral'
id = Column(Integer, primary_key=True)
label = Column(String(20), nullable=False)
__mapper_args__ = {'polymorphic_on': peripheral_type,
'polymorphic_identity': 'peripheral'}
class Actuator(Peripheral):
__tablename__ = 'actuator'
__mapper_args__ = {'polymorphic_identity': 'actuator'}
id = Column(None, ForeignKey('peripheral.id'), primary_key=True)
duration = Column(Integer)
Any suggestion ?
usually relationship() with cascade=all, delete-orphan is used for this use
case, so that SQLAlchemy can maintain knowledge about the link between
Peripheral and Actuator. The other alternative is to use ON DELETE CASCADE
on the foreign key; this is part of the schema you'd generate in the database.
Relevant docs:
http://www.sqlalchemy.org/docs/orm/tutorial.html#configuring-delete-delete-orphan-cascade
http://www.sqlalchemy.org/docs/core/schema.html#on-update-and-on-delete
http://www.sqlalchemy.org/docs/orm/collections.html#using-passive-deletes
Regards,
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Re: [sqlalchemy] Cant understand behavior of sqlalchemy while adding same object twice in a session
On Oct 18, 2011, at 1:21 PM, Manav Goel wrote:
Hello,
I am working in eclipse IDE.
I have this code in the file :
class User(Base):
__tablename__ = 'users'
id = Column('user_id',Integer,primary_key = True)
name = Column('user_name',String(20))
addresses = relationship(Address)
def __repr__(self):
return User(%s) % self.name
session = Session(bind=engine)
u=User('myname')
session.add(u)
session.flush()
print u.id
I ran this file and it worked fine but then I changed
something.
Now to see the effect I have to run file again and then I
noticed this
Instead of adding two different objects with two
different ids but same name. It simply updated the id of already existing
object.
Now I have two questions :
1. What is the reason of this behavior? First of all it should have
made two different objects .
absolutely. the User() object has no primary key assigned and is not the
result of a previous query, so add() will add it as a new row. So the code
above is not the complete story and you'd have to figure out what you're doing
on your end beyond what's illustrated above.
But I think it did not do that because it thought this object is similar to
existing one.
This is not SQLA's behavior. SQLAlchemy does not make guesses about data.
In that case it should have raised exception instead of simply my primary key.
what kind of exception ? its legal to have two objects with the same name here
unless you applied a unique constraint to the user_name column which does not
seem to be the case here.
2. WHat happened when I ran the file again? It created a brand new
session or continued the previous one?
The Session is an instantiation of an object present in memory only within the
Python process. So by definition any new invocation of a Python program begins
with all new state including Session objects.
3. Due to problem mentioned in point no 1. it wasted my early id nos
as when I committed it saved the last one?
I don't know what this means.
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Re: [sqlalchemy] Using collation sequence in SqlAlchemy against Sqlite DB
I don't know what icu_load_collation is, but SQLite's documentation points to
section 6.2, Collation Sequence Examples at
http://www.sqlite.org/datatype3.html which describes how to create tables with
certain collations. There is also the COLLATE operator:
http://www.sqlite.org/lang_expr.html#collateop . Built-in collations described
there include BINARY, NOCASE, and RTRIM, that's it.
Your first step is to determine exactly what SQL you'd like to emit against
your database using the sqlite3 command line utility. Once you've identified
the exact SQL conversation you'd like to have, it can be automated with
SQLAlchemy through various means, possible features here include the func
object as well as the collate function:
http://www.sqlalchemy.org/docs/core/expression_api.html#sqlalchemy.sql.expression.func
http://www.sqlalchemy.org/docs/core/expression_api.html?highlight=collate#sqlalchemy.sql.expression.collate
On Oct 18, 2011, at 1:54 PM, Roja Sen wrote:
Could someone help me to set different collation in sqlAlchemy against
Sqlite DB? I tried to execute something like SELECT
icu_load_collation('pl_PL', 'POLISH') when getting a connection but
couldn't
reference the collation sequence when creating the table object, I
keep
getting the following error.
*sqlite3.OperationalError: no such collation sequence: POLISH*
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[sqlalchemy] How to keep ORM Sessions in sync when using the SQL expression language as well?
I often mix up the SQL expression language with the use of an ORM session, and it is great that SQLAlchemy more than supports this. But... what are the recommended ways to keep the session in sync with what you do with the SQL expression stuff? For example, with the ORM you can't really do a batch/bulk insert (that I know of), but you *can* mix in some SQL expression language to achieve it. Here is a complete example that shows this for the standard Users/Addresses example: http://pastebin.com/BArU6hci In there I do a semi-bulk insert of addresses using both the ORM way and the SQL Expression Language way. With the former way, the inserted addresses are available *with their ids* without ever seeming to have a query emitted to get them. With the latter way (SQLEL) the ORM needed to emit a query to get the addresses (even when I don't ask for id), presumably to update it's identity map. Although the latter behaviour isn't really surprising, can the query be avoided somehow? Is there a way to manually update the session/identity-map with the info? In general, is there a better way to do what I'm doing? The example is obviously a simplified one... my actual use case is batch inserting thousands of records this way and I'd like to be able to keep the ORM and avoid the extra query if I could. -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To view this discussion on the web visit https://groups.google.com/d/msg/sqlalchemy/-/rnzqnwQl858J. 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 at http://groups.google.com/group/sqlalchemy?hl=en.
