Django 事务 : How to run extra code during rollback?

Question

假设您的网络应用中有一个 User 模型，并且您需要通过 API 使该用户与外部服务保持同步。因此，当您在本地创建用户时，您还需要远程创建它。

您的所有操作都在 transaction.atomic() 下，并且您尝试将所有第 3 方 API 调用保留在原子 block 之后，这是合理的。

但是，系统就是一个系统，它会变得越来越复杂，直到您在更新调用中删除一些非常难以删除的第 3 方调用。

也就是说，有没有办法扩展 Django 的事务机制，添加一些回调函数，例如 rollback.add_callback(clean_3rdparty_user(user_id=134))？

这样我就可以保证采取所有必要的回滚操作并且我的系统保持同步？

Answer 1

Django事务钩子(Hook)代码的作者有this to say关于为什么有 on_commit() 但没有 on_rollback():

A rollback hook is even harder to implement robustly than a commit hook, since a variety of things can cause an implicit rollback. For instance, your database connection was dropped because your process was killed without a chance to shutdown gracefully: your rollback hook will never run.

由于回滚通常是由异常触发的，因此一种简单的方法是捕获任何异常并在那里运行撤消代码。

try:
    with transaction.atomic():
        # Do database stuff
        # Do external stuff
except:
    # We know the database stuff has rolled back, so...
    # Undo external stuff
    raise

这并不是特别优雅。我同意以下来自同一来源的观点:

The solution is simple: instead of doing something during the atomic block (transaction) and then undoing it if the transaction fails, use on_commit to delay doing it in the first place until after the transaction succeeds. It’s a lot easier to undo something you never did in the first place!

但听起来你也同意这一点。