Parent instance %s is not bound to a Session; lazy load operation of attribute '%s' cannot proceed

Raise code

self._invoke_raise_load(state, passive, "raise")

        session = _state_session(state)
        if not session:
            if passive & attributes.NO_RAISE:
                return attributes.PASSIVE_NO_RESULT

            raise orm_exc.DetachedInstanceError(
                "Parent instance %s is not bound to a Session; "
                "lazy load operation of attribute '%s' cannot proceed"
                % (orm_util.state_str(state), self.key)
            )

        # if we have a simple primary key load, check the
        # identity map without generating a Query at all
        if u