code: def _sort_by_unique_fields(model, model_objs, unique_fields):
      unique_fields = [
          field for field in model._meta.fields
          if field.attname in unique_fields
      ]
      def sort_key(model_obj):
          return tuple(
              field.get_db_prep_save(getattr(model_obj, field.attname),
                                     connection)
              for field in unique_fields
          )
      return sorted(model_objs, key=sort_key)