Hi,
I have two tables User and Following, and User has two relationships followings
and followers. It’s so typical, and next I want is readonly relationship to
union of followings and followers. I tried like:
friends = relationship(
'User',
collection_class=set,
primaryjoin='''or_(
and_(foreign(User.id) == Following.follower_id,
remote(User.id) == Following.followee_id),
and_(foreign(User.id) == Following.followee_id,
remote(User.id) == Following.follower_id)
)''',
viewonly=True
)
but it seems to no work because foreign_keys and remote_side are the same
columns (User.id). The error message is:
sqlalchemy.exc.ArgumentError: Can't determine relationship direction for
relationship 'User.friends' - foreign key columns within the join condition are
present in both the parent and the child's mapped tables. Ensure that only
those columns referring to a parent column are marked as foreign, either via
the foreign() annotation or via the foreign_keys argument.
Basically I want to find how to specify foreign_keys and remote_side in such
self-referential many-to-many relationships, but it’s okay if there’re any
other ways to implement the same thing. I just need to use such relationship
in query expressions e.g. query.filter(User.friends.any(…)),
query.options(joinedload(User.friends)) and instance properties e.g.
map(make_json, user.friends). (If I implement it using @property decorator it
won’t work with query expressions.)
I read these two chapters in the docs:
http://docs.sqlalchemy.org/en/rel_0_8/orm/relationships.html#self-referential-many-to-many-relationship
http://docs.sqlalchemy.org/en/rel_0_8/orm/relationships.html#creating-custom-foreign-conditions
Are there any other resources to get more hints about it?
Thanks,
Hong Minhee
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