code: func (s *UpdateByQueryService) SortByField(field string, ascending bool) *UpdateByQueryService {
  	if ascending {
  		s.sort = append(s.sort, fmt.Sprintf("%s:asc", field))
  	} else {
  		s.sort = append(s.sort, fmt.Sprintf("%s:desc", field))
  	}
  	return s
  }
docs: // SortByField adds a sort order.