Is there a video or slides from that pycon talk available online? I
see the overview on the pycon site
(http://us.pycon.org/2009/tutorials/schedule/2PM4/) and it looks very
interesting.
I looked more at what you said about the parent id column taking
precedence and that does seem to be what happens. In particular, I see
that the sql generated for
session.query(Child1).filter( Child1.id.in_( range(5))) .count()
uses the IN condition on parent.id in .53, whereas it was on the
child1.id in .48. The .48 behavior seems better here. I can't think of
a situation where I would say Child1.id and want it to use the column
from the parent table instead of the child.
Regardless, now that I understand what is happening, I will be able to
get my application working on .53.
Thanks for your help.
On Wed, Apr 8, 2009 at 6:04 PM, Michael Bayer <mike...@zzzcomputing.com> wrote:
>
> this is a side effect of "declarative" which I covered in my pycon
> tutorial. Child1.id is a map of both "child1.id" and "parent.id", since
> they are mapped under the same name. you can see this if you say
> Child1.id.property.columns. the non-foreign key parent.id takes
> precedence.
>
> the easy solution is to split them up:
>
> class Child1(Parent):
> __tablename__ = 'child1'
> __mapper_args__ = dict(polymorphic_identity = 'child1')
> child_id = Column(Integer, ForeignKey('parent.id'), primary_key=True)
>
>
> class Other(Base):
> __tablename__ = 'other'
> id = Column(Integer, primary_key=True)
> child1_id = Column(Integer, ForeignKey('child1.id'))
> child1_object = relation('Child1', backref='others', primaryjoin =
> child1_id == Child1.child_id)
>
>
>
> Bobby Impollonia wrote:
>>
>> I am porting some code from SQLA .48 to .53 . I have a relation that
>> works in .48, but not in .53.
>>
>> At the end of this post is a test program demonstrating the problem.
>> The program works in .48 but fails in .53 trying to understand the
>> child1_object relation . The error message says to add foreign_keys to
>> the relation, but that doesn't seem to actually help.
>>
>> It does however work if I change the relation to
>> child1_object = relation('Child1', backref='others', primaryjoin =
>> child1_id == Child1.__table__.c.id)
>> Is making this change the recommended solution? Is the behavior I am
>> seeing here expected? Is the message telling me to use foreign_keys
>> bogus?
>>
>> Here is the code:
>>
>> #!/usr/bin/python -u
>> from sqlalchemy import Column, Integer, create_engine, String, ForeignKey
>> from sqlalchemy.orm import sessionmaker, relation
>> from sqlalchemy.ext.declarative import declarative_base
>>
>> Base = declarative_base()
>>
>> class Parent(Base):
>> __tablename__ = 'parent'
>> id = Column(Integer, primary_key=True)
>> _cls = Column('cls', String(50))
>> __mapper_args__ = dict(polymorphic_on = _cls )
>>
>> class Child1(Parent):
>> __tablename__ = 'child1'
>> __mapper_args__ = dict(polymorphic_identity = 'child1')
>> id = Column(Integer, ForeignKey('parent.id'), primary_key=True)
>>
>> class Child2(Parent):
>> __tablename__ = 'child2'
>> __mapper_args__ = dict(polymorphic_identity = 'child2')
>> id = Column(Integer, ForeignKey('parent.id'), primary_key=True)
>>
>> class Other(Base):
>> __tablename__ = 'other'
>> id = Column(Integer, primary_key=True)
>> child1_id = Column(Integer, ForeignKey('child1.id'))
>> child1_object = relation('Child1', backref='others', primaryjoin =
>> child1_id == Child1.id)
>>
>> engine = create_engine('sqlite://')
>> Base.metadata.create_all(engine)
>> session = sessionmaker(engine)()
>>
>> def main():
>> child1 = Child1()
>> child2 = Child2()
>> other = Other()
>> child1.others = [other]
>> session.add(child1)
>> session.add(child2)
>> session.add(other)
>> session.flush()
>> assert 2 == session.query(Parent).count()
>> assert child1 == session.query(Other).one().child1_object
>>
>> if __name__ == '__main__':
>> main()
>>
>> >
>>
>
>
> >
>
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