Django Signals

Built-in Signals

Django provides a set of built-in signals that let user code get notified by Django itself of certain actions. These include some useful notifications:

• django.db.models.signals.pre_save & django.db.models.signals.post_save

  Sent before or after a model’s save() method is called.

• django.db.models.signals.pre_delete & django.db.models.signals.post_delete

  Sent before or after a model’s delete() method or queryset’s delete() method is called.

• django.db.models.signals.m2m_changed

  Sent when a ManyToManyField on a model is changed.

• django.core.signals.request_started & django.core.signals.request_finished

  Sent when Django starts or finishes an HTTP request.

See the built-in signal documentation for a complete list, and a complete explanation of each signal.

Listen to Signals

To receive a signal, register a receiver function using the Signal.connect() method. The receiver function is called when the signal is sent:

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# 函数原型
Signal.connect(receiver, sender=None, weak=True, dispatch_uid=None)
"""
参数说明：
- receiver: 信号发生的回调函数
  See [Receiver functions](https://docs.djangoproject.com/en/2.1/topics/signals/#receiver-functions)

- sender: 指定一个信号的发生者
  See [Connecting to signals sent by specific senders](https://docs.djangoproject.com/en/2.1/topics/signals/#connecting-to-specific-signals)
  
- weak: 暂时没看懂，反正默认是 True 就对了

- dispatch_uid: 在可能发生重复信号的情况下设置接受器的唯一标识
"""