code: def get_unique_fields(self):
          
          for unique_together in self._meta.unique_together:
              if 'sort_order' in unique_together:
                  unique_fields = list(unique_together)
                  unique_fields.remove('sort_order')
                  return ['%s_id' % f for f in unique_fields]
          return []
docs: List field names that are unique_together with `sort_order`.