def refresh(self, fields=None, **kwargs):
        """
        Re get the instance of current id
        """
        cond = self.c[self._primary_field]==self._key
        query = self.filter(cond, **kwargs)
        if not fields:
            fields = list(self.table.c)
        
        v = query.values_one(*fields)
        if not v:
            raise NotFound('Instance <{0}:{1}> can not be found'.format(self.tablename, self._key))
        
        d = self._data_prepare(v.items())
        self.update(**d)
        self.set_saved()
Re get the instance of current id