'Produce a construct that represents a particular \'subtype\' of
attribute for the parent class.
Currently this is usable in conjunction with :meth:`.Query.join`
and :meth:`.Query.outerjoin`.'

def of_type(self, cls):

    return RelationshipProperty.Comparator(self.property, self._parentmapper, adapt_to_entity=self._adapt_to_entity, of_type=cls)
