[FIXED] Flask-SQLAlchemy - model has no attribute 'foreign_keys'

Issue

I have 3 models created with Flask-SQLalchemy: User, Role, UserRole

role.py:

class Role( ActiveRecord, db.Model ):

    __tablename__ = "roles"

    #   Schema
    id = db.Column( db.Integer, primary_key = True )
    name = db.Column( db.String( 24 ), unique = True )
    description = db.Column( db.String( 90 ) )

    users = db.relationship( "User", secondary = "UserRole", \
        backref = db.backref( "roles" ) )

user.py:

class User( db.Model, ActiveRecord ):

    __tablename__ = "users"

    #   Schema
    id = db.Column( db.Integer, primary_key = True )
    email = db.Column( db.String( 90 ), unique = True )
    password = db.Column( db.String( 64 ) )

    #   Relations
    roles = db.relationship( "Role", secondary = "UserRole", \
        backref = db.backref( "users" ) )

user_role.py:

class UserRole( ActiveRecord, db.Model ):

    __tablename__ = "user_roles"

    #   Schema
    user_id = db.Column( db.Integer, db.ForeignKey( 'users.id' ), primary_key = True )
    role_id = db.Column( db.Integer, db.ForeignKey( 'roles.id' ), primary_key = True )

If I try (in the console) to get all users via User.query.all() I get AttributeError: 'NoneType' object has no attribute 'all' and if I try again I get another error saying:

sqlalchemy.exc.InvalidRequestError: One or more mappers failed to initialize - can't proceed with initialization of other mappers.  Original exception was: type object 'UserRole' has no attribute 'foreign_keys'

Can anyone shed a light on what is it exactly that I'm doing wrong? I think I had this code running ok a few months ago, but I updated SQLAlchemy, Flask and Flask-SQLAlchemy recently and it stopped. It's just a side project.

Solution

it's a little tough here because you are using some unknown base classes like "ActiveRecord" and such. However, it looks pretty much like that "secondary" argument is wrong:

class User( db.Model, ActiveRecord ):

    __tablename__ = "users"

    #   Schema
    id = db.Column( db.Integer, primary_key = True )
    email = db.Column( db.String( 90 ), unique = True )
    password = db.Column( db.String( 64 ) )

    #   Relations
    roles = db.relationship( "Role", secondary = "UserRole", \
        backref = db.backref( "users" ) )

secondary needs to refer to a Table object, not a mapped class, if by string name then it would be "user_roles":

    roles = db.relationship( "Role", secondary = "user_roles", \
        backref = db.backref( "users" ) )

Answered By - zzzeek