code: def prepare_sorting_fields(self):
          if self.sorting_parameter_name in self.request.query_params:
              self._sorting_fields = [
                  _.strip() for _ in self.request.query_params.get(self.sorting_parameter_name).split(',')
              ]
          if self._sorting_fields:
              self._sorting_fields = [
                  (self.sorting_fields_map.get(field.lstrip('-'), field.lstrip('-')), field[0] == '-')
                  for field in self._sorting_fields
              ]