SQLAlchemy: foreign keys to declared_attr columns - sqlalchemy

Question

I'm having trouble using the foreign_keys argument with declared_attr columns. My models look like this:
class BasicTable(object):
created = db.Column(db.DateTime)
last_modified = db.Column(db.DateTime)
#declared_attr
def created_by_id(cls):
return db.Column(db.Integer, db.ForeignKey("app_user.id", use_alter = True, name='fk_created_by_id'))
#declared_attr
def created_by(cls):
return db.relationship("AppUser", foreign_keys='{}.{}'.format(cls.__tablename__, 'created_by_id'))
#declared_attr
def last_modified_by_id(cls):
return db.Column(db.Integer, db.ForeignKey("app_user.id", use_alter = True, name='fk_last_modified_by_id'))
#declared_attr
def last_modified_by(cls):
return db.relationship("AppUser", foreign_keys='{}.{}'.format(cls.__tablename__, 'last_modified_by_id'))
class AppUser(BasicTable, db.Model):
id = db.Column(db.Integer, primary_key=True)
email = db.Column(db.String(64))
service_id = db.Column(db.Integer, db.ForeignKey("service.id"))
Because there are two columns in BasicTable that reference AppUser, I was getting "ambiguous foreign keys" errors, so I tried to use the foreign_keys argument as described here. The above gives me this error:
AttributeError: 'Table' object has no attribute 'last_modified_by_id'
When I check the database, that field does exist on all the tables that use BasicTable. Is this error happening because I'm referencing a declared_attr column? This suggests so, but when I tried to use the lambda technique like this:
foreign_keys=lambda: cls.created_by_id
I get this error:
InvalidRequestError: When initializing mapper Mapper|AppUser|app_user, expression 'BasicTable' failed to locate a name ("name 'BasicTable' is not defined"). If this is a class name, consider adding this relationship() to the <class 'app.models.AppUser'> class after both dependent classes have been defined.
Is there a way around this? Thanks!

Answer 1

class BasicTable(object):
created = db.Column(db.DateTime)
last_modified = db.Column(db.DateTime)
#declared_attr
def created_by_id(cls):
return db.Column(db.Integer, db.ForeignKey("app_user.id", use_alter = True, name='fk_created_by_id'))
#declared_attr
def created_by(cls):
return db.relationship('AppUser', primaryjoin='%s.created_by_id==AppUser.id' % cls.__name__,
remote_side='AppUser.id')
#declared_attr
def last_modified_by_id(cls):
return db.Column(db.Integer, db.ForeignKey("app_user.id", use_alter = True, name='fk_last_modified_by_id'))
#declared_attr
def last_modified_by(cls):
return db.relationship('AppUser', primaryjoin='%s.last_modified_by_id==AppUser.id' % cls.__name__,
remote_side='AppUser.id')