I’m facing an issue with SQLAlchemy in my Flask application. I have two models: User and AssignmentReminder. Both models have foreign key relationships with the users.id column in the User model, but I’m getting the following error when I try to run my app:

sqlalchemy.exc.AmbiguousForeignKeysError: Could not determine join condition between parent/child tables on relationship User.assignments

Models:

class User(db.Model):
    __tablename__ = 'users'

    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)
    assignments = db.relationship('AssignmentReminder', backref='user', lazy=True)

class AssignmentReminder(db.Model):
    __tablename__ = 'assignments'

    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(200), nullable=False)
    description = db.Column(db.Text, nullable=False)
    due_date = db.Column(db.Date, nullable=False)
    user_id = db.Column(db.Integer, db.ForeignKey('users.id'), nullable=False)
    recipient_id = db.Column(db.Integer, db.ForeignKey('users.id'), nullable=True)

    creator = db.relationship('User', back_populates='assignments')
    recipient = db.relationship('User', back_populates='assignments_received')

Issue:

I’m getting an AmbiguousForeignKeysError because SQLAlchemy cannot determine which foreign key to use for the relationship between User and AssignmentReminder. Both user_id and recipient_id refer to users.id, but SQLAlchemy doesn’t know which one to use for the assignments relationship.

What I’ve Tried:

• I have defined both user_id and recipient_id as foreign keys that reference the users.id column in the User model.
• I attempted to define relationships in the User model to refer to both assignments and assignments_received, but I’m still encountering the AmbiguousForeignKeysError.
• I tried using foreign_keys in the db.relationship() to explicitly specify which foreign key should be used, but it didn’t resolve the issue.

What I Expected:

• I expected SQLAlchemy to correctly infer the relationship between the User and AssignmentReminder models, given that both user_id and recipient_id are foreign keys referencing users.id.
• I also expected that using foreign_keys in the relationship definition would help SQLAlchemy distinguish between the two foreign keys, resolving the ambiguity.

Question:

How can I fix the AmbiguousForeignKeysError and make sure that SQLAlchemy can correctly resolve the foreign key relationship between User and AssignmentReminder?

Any help would be greatly appreciated!