code: def reload(self):
          
  
          old_doc = self.mongokat_collection.find_one({"_id": self['_id']}, read_use="primary")
  
          if not old_doc:
              raise OperationFailure('Can not reload an unsaved document.'
                                     ' %s is not found in the database. Maybe _id was a string and not ObjectId?' % self['_id'])
          else:
              for k in list(self.keys()):
                  del self[k]
              self.update(dotdict(old_doc))
  
          self._initialized_with_doc = False
docs: allow to refresh the document, so after using update(), it could reload
          its value from the database.
  
          Be carreful : reload() will erase all unsaved values.
  
          If no _id is set in the document, a KeyError is raised.