我坚持使用flask和flask-sqlalchemy从MySQL db中删除多对多记录。似乎 sqlalchemy 试图从关系表中删除所有行，其中 a 的 id 与链接到 b 的 id 相同。
错误（示例）：
sqlalchemy.orm.exc.StaleDataError: DELETE statement on table 'ksiazka_autor' expected to delete 1 row(s); Only 0 were matched.
或者
sqlalchemy.orm.exc.StaleDataError: DELETE statement on table 'ksiazka_wydawnictwo' expected to delete 552 row(s); Only 551 were matched.
INFO sqlalchemy.engine.base.Engine DELETE FROM ksiazka_kategoria WHERE ksiazka_kategoria.ksiazka_id = %s AND ksiazka_kategoria.kategoria_id = %s
2017-08-29 15:44:34,965 INFO sqlalchemy.engine.base.Engine ((166, 40), (167, 40), (168, 40), (169, 40), (170, 40), (171, 40), (172, 40), (173, 40) ... displaying 10 …