On Feb 17, 2010, at 6:15 AM, cropr wrote:
> I have defined a self refential class ContentObject to build a node
> tree wih parent child relationships.
>
> class ContentObject(Base):
> __tablename__ = 'contentobject'
> _contentType = 'contentobject'
> id = Column(types.Integer, primary_key=True, autoincrement=True)
> parent_id = Column(types.Integer, ForeignKey('contentobject.id'))
> type = Column(types.String(32))
> children = relation("ContentObject", backref=backref('parent',
> remote_side=id))
> __mapper_args__ = {'polymorphic_on':type,
> 'polymorphic_identity':'contentobject'}
> ...
>
> Everthing works fine until I define an additional foreign key
> relation between 2 descandant classes of ContentObject.
search the docs for the "inherit_condition" argument to mapper().
>
> class A(ContentObject):
> __tablename__ = 'a'
> __mapper_args__ = {'polymorphic_identity' : 'a'}
> id = Column(types.Integer, ForeignKey(ContentObject.id),
> primary_key=True)
> datum = Column(types.Date)
>
> class B(ContentObject):
> __tablename__ = 'b'
> __mapper_args__ = {'polymorphic_identity' : 'b}
> id = Column(types.Integer, ForeignKey(ContentObject.id),
> primary_key=True)
> linkb_id = Column(types.Integer, ForeignKey(A.id))
> linkb = relation(EloLijst, primaryjoin='b.c.a_id==a.c.id')
>
>
> Now I get the error Can't determine between 'contentobject' and 'b':
> tables have more than one foreign key constraint between them. Specify
> onclause of this join explicitely
>
> How should I do that?
>
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