docs: def sort_by(self, *ids):
          """Update files order.
  
          :param ids: List of ids specifying the final status of the list.
          """
          # Support sorting by file_ids or keys.
          files = {str(f_.file_id): f_.key for f_ in self}
          # self.record['_files'] = [{'key': files.get(id_, id_)} for id_ in ids]
          self.filesmap = OrderedDict([
              (files.get(id_, id_), self[files.get(id_, id_)].dumps())
              for id_ in ids
          ])
          self.flush()