docs: def commit(self, session=None):
          """Merge modified objects into parent transaction.
  
          Once commited a transaction object is not usable anymore
  
          :param:session: current sqlalchemy Session
          """
          if self.__cleared:
              return
  
          if self._parent:
              # nested transaction
              self._commit_parent()
          else:
              self._commit_repository()
          self._clear()