docs: def iterator(self):
          """
          Returns an iterator over all entity states held by this Unit Of Work.
          """
          # FIXME: There is no dependency tracking; objects are iterated in
          #        random order.
          for ent_cls in list(self.__entity_set_map.keys()):
              for ent in self.__entity_set_map[ent_cls]:
                  yield EntityState.get_state(ent)