Hi all,
I've been trying to get the "grandchildren" relationship working in
the code below, but have just about run out of permutations to try. I
couldn't get much out of the docs, and the archives turned up a few
similar queries but none with an answer. Is this even possible? Is
there a better way to accomplish this result (the collection of
related Grandchild objects accessible from an instance of Parent)?
class Parent(Base):
__tablename__ = 'parents'
id = Column(Integer, primary_key=True)
# this works of course
children = relationship('Child', backref='parent')
# but this doesn't
grandchildren = relationship("Grandchild",
primaryjoin="and_(Grandchild.childs_id==Child.id,\
Child.parents_id==Parent.id)",
foreign_keys=['Grandchild.childs_id','Child.parents_id'])
class Child(Base):
__tablename__ = 'childs'
id = Column(Integer, primary_key=True)
parents_id = Column(Integer, ForeignKey("parents.id"))
class Grandchild(Base):
__tablename__ = 'grandchilds'
id = Column(Integer, primary_key=True)
childs_id = Column(Integer, ForeignKey("childs.id"))
This throws an exception:
InvalidRequestError: One or more mappers failed to compile. Exception
was probably suppressed within a hasattr() call. Message was: Could
not determine relationship direction for primaryjoin condition
'grandchilds.childs_id = childs.id AND childs.parents_id =
parents.id', on relationship Parent.grandchildren. Specify the
'foreign_keys' argument to indicate which columns on the relationship
are foreign.
Thanks for any help,
Anders
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