"""

    在web开发中, 你可能会遇到下面这种场景:

    在用户完成某个操作后, 自动去执行一些后续的操作. 譬如用户完成修改密码后,你要发送一份确认邮件

    观察者模式：观察者模式(Observer)完美的将观察者和被观察的对象分离开。

        举个例子，用户界面可以作为一个观察者，业务数据是被观察者，

        用户界面观察业务数据的变化，发现数据变化后，就显示在界面上

"""

"""学习网站https://simpleisbetterthancomplex.com/tutorial/2016/07/28/how-to-create-django-signals.html"""

"""两个重要的对象：Sender receiver

         sender dispatch a signal, receiver receive signal and do something

         sender 是一个object, receiver是一个方法，或者对象的方法

         将sender和receiver关联起来是通过signal dispatchers, 即Signal.connect()方法来关联sender,receiver

"""

# post_save信号

""" 在mode对象执行save函数时，就会触发该信号"""

from django.contrib.auth.models import User

from django.db.models.signals import post_save

def save_profile(sender, instance, **kwargs):

    instance.profile.save()

post_save.connect(save_profile, sender=User)

# save_profile是receiver，User是sender, post_save是signal, 上面代码可以理解成：当User对象执行save函数后，就会执行save_profile函数

# 如果去掉post_save.connect的sender参数，如： post_save.connect(save_profile)， 则就是任意一个model执行了save函数，都会调用save_profile函数

"""关联sender和receiver还可以通过@receiver装饰器来完成

def receiver(signal, **kwargs)"""

# 两个参数，signal可以是元组或者列表，或者单个信号

# **kwargs是位置参数，注意

from django.contrib.auth.models import User

from django.db.models.signals import post_save

from django.dispatch import receiver

@receiver(post_save, sender=User)

def save_profile(sender, instance, **kwargs):

    instance.profile.save()

# 注册信号不应该在app的models或者根目录，django建议我们将signals放到config里面，以下面为了，profile为一个app；cmdbox是project

# profile/signals.py

from django.contrib.auth.models import User

from django.db.models.signals import post_save

from django.dispatch import receiver

from cmdbox.profiles.models import Profile

@receiver(post_save, sender=User)

def create_user_profile(sender, instance, created, **kwargs):

    if created:

        Profile.objects.create(user=instance)

@receiver(post_save, sender=User)

def save_user_profile(sender, instance, **kwargs):

    instance.profile.save()

""" instance参数就是sender的实例化对象"""

#profiles/app.py:

from django.apps import AppConfig

from django.utils.translation import ugettext_lazy as _

class ProfilesConfig(AppConfig):

    name = 'cmdbox.profiles'

    verbose_name = _('profiles')

    def ready(self):

        import cmdbox.profiles.signals  # noqa

# profiles/__init__.py: 如果已经在工程里面注册了app,这里是不需要的

default_app_config = 'cmdbox.profiles.apps.ProfilesConfig'

# 如果是通过connect关联sender和receiver,参考下面代码

# profile/signals.py

from cmdbox.profiles.models import Profile

def create_user_profile(sender, instance, created, **kwargs):

    if created:

        Profile.objects.create(user=instance)

def save_user_profile(sender, instance, **kwargs):

    instance.profile.save()

# profile/app.py

from django.apps import AppConfig

from django.contrib.auth.models import User

from django.db.models.signals import post_save

from django.utils.translation import ugettext_lazy as _

from cmdbox.profiles.signals import create_user_profile, save_user_profile

class ProfilesConfig(AppConfig):

    name = 'cmdbox.profiles'

    verbose_name = _('profiles')

    def ready(self):

        post_save.connect(create_user_profile, sender=User)

        post_save.connect(save_user_profile, sender=User)

# profiles/__init__.py:

default_app_config = 'cmdbox.profiles.apps.ProfilesConfig'