2 relationships of the same tablename confusing SQLAlchemy

Question

IE:

class Share(db.Model):
    """
    Stores the Checkpoint shares between users
    """
    id = db.Column(db.Integer, primary_key=True)
    user_from_id = db.Column(db.Integer, db.ForeignKey('user.id'))
    user_from = db.relationship("User")
    user_to_id = db.Column(db.Integer, db.ForeignKey('user.id'))
    user_to = db.relationship("User")

I get an error:

ArgumentError: Could not determine join condition between parent/child tables on relationship Share.user_from. Specify a 'primaryjoin' expression. If 'secondary' is present, 'secondaryjoin' is needed as well.

How can I fix this?

Thanks!

Answer 1

As the error message suggests, you need to specify primaryjoin value for your relationships:

class Share(db.Model):
    # ...
    user_from = relationship("User", primaryjoin="Share.user_from_id==User.id")
    user_to = relationship("User", primaryjoin="Share.user_to_id==User.id")
    # ...

See Specifying Alternate Join Conditions to relationship() for more information.