code: def prefetch_related(self, *args: str) -> "QuerySet":
          
          queryset = self._clone()
          queryset._prefetch_map = {}
  
          for relation in args:
              if isinstance(relation, Prefetch):
                  relation.resolve_for_queryset(queryset)
                  continue
              relation_split = relation.split("__")
              first_level_field = relation_split[0]
              if first_level_field not in self.model._meta.fetch_fields:
                  raise FieldError(
                      "relation {} for {} not found".format(first_level_field, self.model._meta.table)
                  )
              if first_level_field not in queryset._prefetch_map.keys():
                  queryset._prefetch_map[first_level_field] = set()
              forwarded_prefetch = "__".join(relation_split[1:])
              if forwarded_prefetch:
                  queryset._prefetch_map[first_level_field].add(forwarded_prefetch)
          return queryset
docs: Like ``.fetch_related()`` on instance, but works on all objects in QuerySet.