Adrian <adr...@planetcoding.net> wrote:
> > the model here doesn’t illustrate how this would be a many-to-many.
> A User can have any number of other Users as a favorite. That looks quite
> many-to-many to me….
then you are referring to a self-referential User -> favorite_user -> User
relationship which is M2M but then I don’t see why you need all the
complexity of using a mixin for a “FavoriteUser”.
> This is a simplified version of my structure:
>
> User:
> - serial id (pk)
> - bool is_deleted
>
> FavoriteUser
> - user_id (pk, fk to User.id)
> - target_id (pk, fk to User.id)
>
> > yeah that’s the lambda + string together which is not the correct use.
> If i put just a string I get the same:
> sqlalchemy.exc.ArgumentError: Column-based expression object expected for
> argument 'primaryjoin'; got: '(User.id == user_id) & ~target.is_deleted',
> type <type 'unicode'>
> With a lamda there error is gone though. That's one step closer :)
There’s no way you get that error unless you still have a lambda + string
together, provided the class is mapped with declarative. The relationship
will pass using a form such as:
@declared_attr
def user(cls):
"""The user owning this favorite"""
return relationship(
'User',
lazy=False,
foreign_keys=lambda: [cls.user_id],
backref=backref(
'_favorite_{}'.format(cls._type),
lazy=True,
cascade='all, delete-orphan',
primaryjoin=lambda: (User.id == cls.user_id) & ~User.is_deleted
)
)
>
> I guess with the way I have my relationships setup at the moment, I'd need to
> access the join from the `target` relationship from the backref of the `user`
> relationship?
>
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