On May 7, 2008, at 7:23 PM, Bobby Impollonia wrote:
>
> secondary_table = Table('secondary', Base.metadata,
> Column('left_id', Integer, ForeignKey('parent.id'),
> nullable=False),
> Column('right_id', Integer, ForeignKey('parent.id'),
> nullable=False))
>
> class Parent(Base):
> __tablename__ = 'parent'
> id = Column(Integer, primary_key=True)
> cls = Column(String(50))
> __mapper_args__ = dict(polymorphic_on = cls )
>
> class Child1(Parent):
> __tablename__ = 'child1'
> id = Column(Integer, ForeignKey('parent.id'), primary_key=True)
> __mapper_args__ = dict(polymorphic_identity = 'child1',
> inherit_condition=Parent.id==id)
>
> class Child2(Parent):
> __tablename__ = 'child2'
> id = Column(Integer, ForeignKey('parent.id'), primary_key=True)
> __mapper_args__ = dict(polymorphic_identity = 'child2')
>
> Child1.left_child2 = relation(Child2, secondary = secondary_table,
> primaryjoin = Child1.c.id == secondary_table.c.right_id,
> secondaryjoin = Child2.c.id == secondary_table.c.left_id,
> uselist = False,
> foreign_keys = [secondary_table.c.left_id,
> secondary_table.c.right_id],
> backref = 'the_backref')
>
> The first time I try to create an object or do a query, I get:
> <class 'sqlalchemy.exceptions.ArgumentError'>: Could not determine
> relation direction for primaryjoin condition 'child2.id =
> secondary.left_id', on relation Child2.the_backref (Child1). Specify
> the foreign_keys argument to indicate which columns on the relation
> are foreign.
when you specify primaryjoin/secondaryjoin to relation(), those
arguments are not copied into the backref automatically, since you've
gone explicit (perhaps this should be adjusted in 0.5). So you need
to use backref=backref('the_backref', primaryjoin=<join>,
secondaryjoin=<otherjoin>, secondary=<table>, foreign_keys=<keys>) in
this case.
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