Thank you. That does the trick.
Till
On Tue, Aug 13, 2013 at 10:54 PM, Simon King <si...@simonking.org.uk> wrote:
> On Tue, Aug 13, 2013 at 2:07 PM, till.plewe <till.pl...@gmail.com> wrote:
>> I am using python 3.3 and sqlalchemy 0.8.2
>>
>> I am trying to define a self-referential many-to-many relationship for a
>> class where the primary key is provided by a mixin. Defining the primary
>> directly in the class works. Using the mixin does not.
>>
>> I would be grateful for any suggestions or pointers to relevant
>> documentation.
>>
>> Below is an example showing my problem. As given the example works.
>> Uncommenting the line "#id = ..." in 'Base' and commenting out the
>> corresponding line in 'A' breaks the example. Is there any way to define
>> the primary key in Base and getting the 'requires' relation to work?
>>
>> -----------------------------------
>>
>> from sqlalchemy import Column, Integer, String, DateTime, Table,
>> ForeignKey,create_engine
>> from sqlalchemy.ext.declarative import declarative_base,declared_attr
>> from sqlalchemy.orm import sessionmaker, relationship, backref
>>
>> class Base(object):
>> #id = Column(Integer, primary_key=True)
>> pass
>>
>> Base = declarative_base(cls=Base)
>>
>> association_table = Table('association',
>> Base.metadata,
>> Column('prerequisite', Integer,
>> ForeignKey('a.id')),
>> Column('dependency', Integer, ForeignKey('a.id')))
>>
>> class A(Base):
>> __tablename__ = "a"
>> id = Column(Integer, primary_key=True)
>> requires = relationship("A",
>> secondary = association_table,
>>
>> primaryjoin=(id==association_table.c.prerequisite),
>>
>> secondaryjoin=(id==association_table.c.dependency),
>> backref = backref("required_by"))
>>
>> if __name__ == "__main__":
>> engine = create_engine('sqlite:///:memory:', echo=False)
>> Session = sessionmaker(bind=engine)
>> session = Session()
>> Base.metadata.create_all(engine)
>>
>> T=A()
>> U=A()
>> session.add(T)
>> session.add(U)
>> T.requires.append(U)
>> session.commit()
>> print("T",T.id,T.requires,T.required_by)
>> print("U",U.id,U.requires,U.required_by)
>>
>
> You can make it work by using strings as the primaryjoin and
> secondaryjoin parameters and referring to A.id rather than just id:
>
> class A(Base):
> __tablename__ = "a"
> requires = relationship("A",
> secondary = association_table,
>
> primaryjoin="A.id==association.c.prerequisite",
>
> secondaryjoin="A.id==association.c.dependency",
> backref = backref("required_by"))
>
> This technique is described in the "Configuring Relationships" section
> of the declarative documentation:
>
> http://docs.sqlalchemy.org/en/rel_0_8/orm/extensions/declarative.html#configuring-relationships
>
> Hope that helps,
>
> Simon
>
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