def _is_ndb(self):
<EOL>if isinstance(self._model, type):<EOL><INDENT>if _NDB_MODEL is not None and issubclass(self._model, _NDB_MODEL):<EOL><INDENT>return True<EOL><DEDENT>elif issubclass(self._model, db.Model):<EOL><INDENT>return False<EOL><DEDENT><DEDENT>raise TypeError(<EOL>'<STR_LIT>'.format(self._model))<EOL>
Determine whether the model of the instance is an NDB model.

        Returns:
            Boolean indicating whether or not the model is an NDB or DB model.