def User():
    from app import db
    class User(db.Model):
        __table_args__ = ({'extend_existing': True})
        id = db.Column(db.Integer, primary_key=True)
        username = db.Column(db.String(15), unique=True)
        email = db.Column(db.String(50), unique=True)
        password = db.Column(db.String(80))
    return User()