def session_mapper(scoped_session):
    def mapper(cls, *arg, **kw):
        cls.query = scoped_session.query_property()
        return sqla_mapper(cls, *arg, **kw)
    return mapper
 
mapper = session_mapper(Session)
 
# Then, you can do like Book.query.get(id) or User.query.filter_by(username="bar")