I just came across a solution to this problem. Adding 'with_polymorphic': '*' to __mapper_args__ on the Node model was enough.
class Node(db.Model): id = db.Column(db.Integer, primary_key=True) type = db.Column(db.String(20)) name = db.Column(db.String(30), nullable=False) date_added = db.Column(db.DateTime, default=datetime.now()) parent_id = db.Column(db.Integer, db.ForeignKey('node.id'), nullable=True ) path = db.Column(db.String(200), default='') __mapper_args__ = {'polymorphic_on': type, 'with_polymorphic': '*' } -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.