'A non-attr_obj store (ndb: NonDataBase). Everything stored
to this is guaranteed to be cleared when a server is shutdown.
Syntax is same as for the _get_db_holder() method and
property, e.g. obj.ndb.attr = value etc.'

def __ndb_get(self):

    try:
        return self._ndb_holder
    except AttributeError:
        self._ndb_holder = DbHolder(self, 'nattrhandler', manager_name='nattributes')
        return self._ndb_holder
