special.py 文件源码

def database_backwards(self, app_label, schema_editor, from_state, to_state):
        if self.reverse_sql is None:
            raise NotImplementedError("You cannot reverse this operation")
        if router.allow_migrate(schema_editor.connection.alias, app_label, **self.hints):
            self._run_sql(schema_editor, self.reverse_sql)