code: def save(self) -> sql.Executant:
          
          r = self._dict_to_SQL(self.modifications)
          self.modifications.clear()
          return r
docs: Prepare a SQL request to save the current modifications.
          Returns actually a LIST of requests (which may be of length one).
          Note than it can include modifications on other part of the data.
          After succes, the base should be updated.