@classmethod
def list_obj(cls, criteria, skip=None, first=None, configname='default'):
    """ find all object with the given search criteria.
            The return value is generator. Each next call will
            fetch a new instance and return it as object.
        """
    for uuid, in cls.list(criteria, ('_uuid',), skip, first, configname):
        yield cls(uuid=uuid)
