code: def refetch_fields(self, missing_fields):
          
          db_fields = self.mongokat_collection.find_one({"_id": self["_id"]}, fields={k: 1 for k in missing_fields})
  
          self._fetched_fields += tuple(missing_fields)
  
          if not db_fields:
              return
  
          for k, v in db_fields.items():
              self[k] = v
docs: Refetches a list of fields from the DB