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Django-signal组件 ​

Django4.2信号官档：https://docs.djangoproject.com/zh-hans/4.2/ref/signals/#signals

Django有一个"信号调度器(signal dispatcher)"。其实就是观察者模式，又叫发布-订阅(Publish/Subscribe) 。当发生一些动作的时候，发出信号，然后监听了这个信号的函数就会执行。

通俗来讲，就是一些动作发生的时候，信号允许特定的发送者去提醒一些接受者。用于在框架执行操作时解耦。

1 自定义信号 ​

  • 定义信号

    python
    import django.dispatch

# 自定义信号
cut_info_signal = django.dispatch.Signal()

  • 注册回调

    python
    from utils.signals import cut_info_signal


def callback_1(sender, **kwargs):
    print("callback-1")


def callback_2(sender, **kwargs):
    print("callback-2")


cut_info_signal.connect(callback_1)
cut_info_signal.connect(callback_2)

  • 触发信号

    python
    from utils.signals import cut_info_signal
cut_info_signal.send("触发了此信号")

将某些动作都注册在一个信号中，一旦达到条件则触发信号(所有回调都执行)。

2 内置信号 ​

Python
Model signals
    pre_init                    # django的model执行其构造方法前，自动触发
    post_init                   # django的model执行其构造方法后，自动触发
    pre_save                    # django的model对象保存前，自动触发
    post_save                   # django的model对象保存后，自动触发
    pre_delete                  # django的model对象删除前，自动触发
    post_delete                 # django的model对象删除后，自动触发
    m2m_changed                 # django的model中使用m2m字段操作第三张表
                                # （add,remove,clear）前后，自动触发
    class_prepared              # 程序启动时，检测已注册的app中model类，对于每一个类，自动触发
    
Management signals
    pre_migrate                 # 执行migrate命令前，自动触发
    post_migrate                # 执行migrate命令后，自动触发
    
Request/response signals
    request_started             # 请求到来前，自动触发
    request_finished            # 请求结束后，自动触发
    got_request_exception       # 请求异常后，自动触发
    
Test signals
    setting_changed             # 使用test测试修改配置文件时，自动触发
    template_rendered           # 使用test测试渲染模板时，自动触发
    
Database Wrappers
    connection_created          # 创建数据库连接时，自动触发

用法一：函数名作为参数注册信号 ​

  • 注册信号回调

    python
    from django.core.signals import request_finished
from django.core.signals import request_started
from django.core.signals import got_request_exception

from django.db.models.signals import class_prepared
from django.db.models.signals import pre_init, post_init
from django.db.models.signals import pre_save, post_save
from django.db.models.signals import pre_delete, post_delete
from django.db.models.signals import m2m_changed
from django.db.models.signals import pre_migrate, post_migrate

from django.test.signals import setting_changed
from django.test.signals import template_rendered

from django.db.backends.signals import connection_created


def func1(*args, **kwargs):
    print("func1")


def func2(*args, **kwargs):
    print("func2")


post_save.connect(func1)
post_save.connect(func2)

  • 触发信号

    python
    from app01 import models

def demo(request):
    models.UserInfo.objects.create(name="wilson", age=21)
    return HttpResponse("OK")

image-20240519092650759

当然，我们将args和kwargs打印出来就可以看到两个信号都是由UserInfo表触发的

image-20240519093115406

用法二：使用装饰器 ​

python
from app01 import models
from django.http import HttpResponse
from django.db.models.signals import post_save


@post_save.connect
def func1(*args, **kwargs):
    print("func1", args, kwargs)


@post_save.connect
def func2(*args, **kwargs):
    print("func2", args, kwargs)


# post_save.connect(func1)
# post_save.connect(func2)


def demo(request):
    models.UserInfo.objects.create(name="wilson", age=21)
    return HttpResponse("OK")

image-20240519093455450

注意信号定义位置 ​

信号的定义和注册我们一般不放在视图函数中，转而放在项目根目录的__init__.py文件中（只要项目启动，该文件会自动加载）

3 内置信号的用法示例 ​

新增模型类对象，触发的相关信号 ​

  • views.py
python
from django.shortcuts import render, HttpResponse
from api.models import User



# ----------- 内置信号的用法 --------------
def index(request):
    # 什么时候模型类对象调用save方法？答案是创建对象的时候，和更新对象的时候
    obj = User.objects.create(name='zhangsan')
    print(obj)
    return HttpResponse("INDEX")
  • demo/__init__.py
python
from django.db.models.signals import pre_init, post_init, pre_save, post_save, pre_delete, post_delete
from django.dispatch import receiver

@receiver(pre_init)
def pre_init_callback(sender, **kwargs):
    """ 每当实例化一个 Django 模型时，这个信号都会在模型的 __init__() 方法的开头发出 """
    print('pre_init_callback', sender)
    print('pre_init_callback', kwargs)

@receiver(post_init)
def post_init_callback(sender, **kwargs):
    """ 和 pre_init 一样，但这个是在 __init__() 方法完成后发送的 """
    print('post_init_callback', sender)
    print('post_init_callback', kwargs)

@receiver(pre_save)
def pre_save_callback(sender, **kwargs):
    """ 这是在模型的 save() 方法开始时发送的 """
    print('pre_save_callback', sender)
    print('pre_save_callback', kwargs)
    print('pre_save_callback', kwargs['instance'].name)


@receiver(post_save)
def post_save_callback(sender, **kwargs):
    """ 就像 pre_save 一样，但在 save() 方法的最后发送 """
    print('post_save_callback', sender)
    print('post_save_callback', kwargs)
    print('post_save_callback', kwargs['instance'].name)

打印效果：

bash
pre_init_callback <class 'api.models.User'>
pre_init_callback {'signal': <django.db.models.signals.ModelSignal object at 0x00000159F5287DC0>, 'args': (), 'kwargs': {'name': 'zhangsan'}}
post_init_callback <class 'api.models.User'>
post_init_callback {'signal': <django.db.models.signals.ModelSignal object at 0x00000159F5287EE0>, 'instance': <User: zhangsan>}
pre_save_callback <class 'api.models.User'>
pre_save_callback {'signal': <django.db.models.signals.ModelSignal object at 0x00000159F5287FD0>, 'instance': <User: zhangsan>, 'raw': False, 'using': 'default', 'update_fields': None}
pre_save_callback zhangsan
post_save_callback <class 'api.models.User'>
post_save_callback {'signal': <django.db.models.signals.ModelSignal object at 0x00000159F52C4100>, 'instance': <User: zhangsan>, 'created': True, 'update_fields': None, 'raw': False, 'using': 'default'}
post_save_callback zhangsan
zhangsan

编辑模型类对象，触发的相关信号 ​

views.py:

python
from django.shortcuts import render, HttpResponse
from api.models import User

# ----------- 内置信号的用法 --------------
def index(request):
    # 什么时候模型类对象调用save方法？答案是创建对象的时候，和更新对象的时候
    # 新增
    # obj = User.objects.create(name='zhangsan')
    # print(obj)

    # 编辑
    obj = User.objects.filter(name='zhangsan2').first()
    old = obj.name
    obj.name = "zhangsan888"
    new = obj.name
    # log.info(f'{old}-->{new}')
    obj.save()

    return HttpResponse("INDEX")

demo/__init__.py：

python
from django.db.models.signals import pre_init, post_init, pre_save, post_save, pre_delete, post_delete
from django.dispatch import receiver

@receiver(pre_init)
def pre_init_callback(sender, **kwargs):
    """ 每当实例化一个 Django 模型时，这个信号都会在模型的 __init__() 方法的开头发出 """
    print('pre_init_callback', sender)
    print('pre_init_callback', kwargs)


@receiver(post_init)
def post_init_callback(sender, **kwargs):
    """ 和 pre_init 一样，但这个是在 __init__() 方法完成后发送的 """
    print('post_init_callback', sender)
    print('post_init_callback', kwargs)


@receiver(pre_save)
def pre_save_callback(sender, **kwargs):
    """ 这是在模型的 save() 方法开始时发送的 """
    print('pre_save_callback', sender)
    print('pre_save_callback', kwargs)
    print('pre_save_callback', kwargs['instance'].name)


@receiver(post_save)
def post_save_callback(sender, **kwargs):
    """ 就像 pre_save 一样，但在 save() 方法的最后发送 """
    print('post_save_callback', sender)
    print('post_save_callback', kwargs)
    print('post_save_callback', kwargs['instance'].name)

日志：

bash
pre_init_callback <class 'api.models.User'>
pre_init_callback {'signal': <django.db.models.signals.ModelSignal object at 0x00000186F4937DC0>, 'args': (1, 'zhangsan2'), 'kwargs': {}}
post_init_callback <class 'api.models.User'>
post_init_callback {'signal': <django.db.models.signals.ModelSignal object at 0x00000186F4937EE0>, 'instance': <User: zhangsan2>}
zhangsan2
pre_save_callback <class 'api.models.User'>
pre_save_callback {'signal': <django.db.models.signals.ModelSignal object at 0x00000186F4937FD0>, 'instance': <User: zhangsan888>, 'raw': False, 'using': 'default', 'update_fields': None}
pre_save_callback zhangsan888
post_save_callback <class 'api.models.User'>
post_save_callback {'signal': <django.db.models.signals.ModelSignal object at 0x00000186F4974100>, 'instance': <User: zhangsan888>, 'created': False, 'update_fields': None, 'raw': False, 'using': 'default'}
post_save_callback zhangsan888

删除模型类对象，触发的相关信号 ​

views.py:

python
from django.shortcuts import render, HttpResponse
from api.models import User



# ----------- 内置信号的用法 --------------

def index(request):
    # 什么时候模型类对象调用save方法？答案是创建对象的时候，和更新对象的时候
    # 新增
    # obj = User.objects.create(name='zhangsan')
    # print(obj)

    # 编辑
    # obj = User.objects.filter(name='zhangsan2').first()
    # old = obj.name
    # obj.name = "zhangsan888"
    # new = obj.name
    # # log.info(f'{old}-->{new}')
    # obj.save()

    # 删除
    obj_list = User.objects.filter(name='zhangsan888')
    # print(111, obj_list)  # <QuerySet [<User: zhangsan888>, <User: zhangsan888>, <User: zhangsan888>]>
    for obj in obj_list:
        obj.delete()

    return HttpResponse("INDEX")

demo/__init__.py：

python
from django.db.models.signals import pre_init, post_init, pre_save, post_save, pre_delete, post_delete
from django.dispatch import receiver

@receiver(pre_init)
def pre_init_callback(sender, **kwargs):
    """ 每当实例化一个 Django 模型时，这个信号都会在模型的 __init__() 方法的开头发出 """
    print('pre_init_callback', sender)
    print('pre_init_callback', kwargs)


@receiver(post_init)
def post_init_callback(sender, **kwargs):
    """ 和 pre_init 一样，但这个是在 __init__() 方法完成后发送的 """
    print('post_init_callback', sender)
    print('post_init_callback', kwargs)





@receiver(pre_save)
def pre_save_callback(sender, **kwargs):
    """ 这是在模型的 save() 方法开始时发送的 """
    print('pre_save_callback', sender)
    print('pre_save_callback', kwargs)
    print('pre_save_callback', kwargs['instance'].name)


@receiver(post_save)
def post_save_callback(sender, **kwargs):
    """ 就像 pre_save 一样，但在 save() 方法的最后发送 """
    print('post_save_callback', sender)
    print('post_save_callback', kwargs)
    print('post_save_callback', kwargs['instance'].name)


@receiver(pre_delete)
def pre_delete_callback(sender, **kwargs):
    """ 在模型的 delete() 方法和查询集的 delete() 方法开始时发送 """
    print('pre_delete_callback', sender)
    print('pre_delete_callback', kwargs)


@receiver(post_delete)
def post_delete_callback(sender, **kwargs):
    """ 就像 pre_delete 一样，但在模型的 delete() 方法和查询集的 delete() 方法结束时发送 """
    print('post_delete_callback', sender)
    print('post_delete_callback', kwargs)

日志：

bash
post_init_callback {'signal': <django.db.models.signals.ModelSignal object at 0x0000026FD6FE7EE0>, 'instance': <User: zhangsan888>}
pre_delete_callback <class 'api.models.User'>
pre_delete_callback {'signal': <django.db.models.signals.ModelSignal object at 0x0000026FD70241F0>, 'instance': <User: zhangsan888>, 'using': 'default', 'origin': <User: zhangsan888>}
post_delete_callback <class 'api.models.User'>
post_delete_callback {'signal': <django.db.models.signals.ModelSignal object at 0x0000026FD70242E0>, 'instance': <User: zhangsan888>, 'using': 'default', 'origin': <User: zhangsan888>}
pre_delete_callback <class 'api.models.User'>
pre_delete_callback {'signal': <django.db.models.signals.ModelSignal object at 0x0000026FD70241F0>, 'instance': <User: zhangsan888>, 'using': 'default', 'origin': <User: zhangsan888>}
post_delete_callback <class 'api.models.User'>
post_delete_callback {'signal': <django.db.models.signals.ModelSignal object at 0x0000026FD70242E0>, 'instance': <User: zhangsan888>, 'using': 'default', 'origin': <User: zhangsan888>}
pre_delete_callback <class 'api.models.User'>
pre_delete_callback {'signal': <django.db.models.signals.ModelSignal object at 0x0000026FD70241F0>, 'instance': <User: zhangsan888>, 'using': 'default', 'origin': <User: zhangsan888>}
post_delete_callback <class 'api.models.User'>
post_delete_callback {'signal': <django.db.models.signals.ModelSignal object at 0x0000026FD70242E0>, 'instance': <User: zhangsan888>, 'using': 'default', 'origin': <User: zhangsan888>}

4 migrate信号应用 ​

当我们执行python manage.py makemigrations和python manage.py migrate后，会自动生成两张有数据的表django_content_type和auth_permission

image-20240519095757844

其实现原理就是，在Django启动时，会在post_migrate信号中注册函数，当我们执行python manage.py migrate时，Django除了会根据已注册的app中migrations文件夹中的配置创建表，还会执行post_migrate信号中注册的函数，向django_content_type和auth_permission表中新增数据

我们可以在Django-auth组件中找到源码：

image-20240519100413069

流程图：

image-20240519101823131

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