Django post_save防止递归而不覆盖模型save()

Question

有许多关于使用post_save信号递归的Stack Overflow帖子,评论和答案都是压倒性的:"为什么不覆盖save()"或者只是触发的保存created == True.

我相信不使用的好例子save()- 例如,我正在添加一个临时应用程序来处理与Order模型完全分开的订单履行数据.

框架的其余部分幸福地没有意识到实现应用程序,并且使用post_save挂钩从我们的订单模型中隔离所有与履行相关的代码.

如果我们放弃履行服务,我们的核心代码就不得不改变.我们删除了履行应用程序,就是这样.

那么,是否有任何不错的方法来确保post_save信号不会两次触发相同的处理程序？

Answer 1

您可以使用更新而不是保存在信号处理程序中

queryset.filter(pk=instance.pk).update(....)

Answer 2

不要断开信号.如果在信号断开时生成任何相同类型的新模型,则不会触发处理函数.信号在Django中是全局的,并且可以同时运行多个请求,使得一些请求失败而其他请求运行其post_save处理程序.

Answer 3

您对此解决方案的看法如何？

@receiver(post_save, sender=Article)
def generate_thumbnails(sender, instance=None, created=False, **kwargs):

    if not instance:
        return

    if hasattr(instance, '_dirty'):
        return

    do_something()

    try:
        instance._dirty = True
        instance.save()
    finally:
        del instance._dirty

您还可以创建装饰器

def prevent_recursion(func):

    @wraps(func)
    def no_recursion(sender, instance=None, **kwargs):

        if not instance:
            return

        if hasattr(instance, '_dirty'):
            return

        func(sender, instance=instance, **kwargs)

        try:
            instance._dirty = True
            instance.save()
        finally:
            del instance._dirty

    return no_recursion


@receiver(post_save, sender=Article)
@prevent_recursion
def generate_thumbnails(sender, instance=None, created=False, **kwargs):

    do_something()

Answer 4

我认为save_without_signals()在模型上创建方法更明确:

class MyModel()
    def __init__():
        # Call super here.
        self._disable_signals = False

    def save_without_signals(self):
        """
        This allows for updating the model from code running inside post_save()
        signals without going into an infinite loop:
        """
        self._disable_signals = True
        self.save()
        self._disable_signals = False

def my_model_post_save(sender, instance, *args, **kwargs):
    if not instance._disable_signals:
        # Execute the code here.

Answer 5

如何断开然后重新连接post_save函数内的信号:

def my_post_save_handler(sender, instance, **kwargs):
    post_save.disconnect(my_post_save_handler, sender=sender)
    instance.do_stuff()
    instance.save()
    post_save.connect(my_post_save_handler, sender=sender)
post_save.connect(my_post_save_handler, sender=Order)