如何在抽象模型中使用Django信号？

I have an abstract model that keeps an on-disk cache. When I delete the model, I need it to delete the cache. I want this to happen for every derived model as well.

我有一个保持磁盘缓存的抽象模型。当我删除模型时，我需要它来删除缓存。我希望每个派生模型都能实现这一点。

If I connect the signal specifying the abstract model, this does not propagate to the derived models:

如果我连接指定抽象模型的信号，则不会传播到派生模型：

pre_delete.connect(clear_cache, sender=MyAbstractModel, weak=False)

If I try to connect the signal in an init, where I can get the derived class name, it works, but I'm afraid it will attempt to clear the cache as many times as I've initialized a derived model, not just once.

如果我尝试在init中连接信号，在那里我可以获得派生类名，它可以工作，但我担心它会尝试清除缓存，因为我已经多次初始化派生模型，而不是一次。

Where should I connect the signal?

我应该在哪里连接信号？

3 个解决方案

#1

Create a custom manager for your model. In its contribute_to_classmethod, have it set a signal for class_prepared. This signal calls a function which binds more signals to the model.

为您的模型创建自定义管理器。在其contrib_to_class方法中，让它为class_prepared设置一个信号。该信号调用将更多信号绑定到模型的函数。

#2

I think you can connect to post_delete without specifying sender, and then check if actual sender is in list of model classes. Something like:

我认为您可以在不指定发件人的情况下连接到post_delete，然后检查实际发件人是否在模型类列表中。就像是：

def my_handler(sender, **kwargs):
    if sender.__class__ in get_models(someapp.models):
        ...

Obviously you'll need more sophisticated checking etc, but you get the idea.

显然你需要更复杂的检查等，但你明白了。

#3

Building upon Justin Lilly's answer, I've created a custom manager that binds a post_save signal to every child of a class, be it abstract or not.

基于Justin Lilly的回答，我创建了一个自定义管理器，它将post_save信号绑定到一个类的每个子节点，无论是抽象的还是不抽象的。

This is a one-off, poorly tested code, so beware! It works so far, though.

这是一次性的，测试不佳的代码，所以要小心！但它到目前为止工作。

In this example, we allow an abstract model to define CachedModelManager as a manager, which then extends basic caching functionality to the model and its children. It allows you to define a list of volatile keys that should be deleted upon every save (hence the post_save signal) and adds a couple of helper functions to generate cache keys, as well as retrieving, setting and deleting keys.

在此示例中，我们允许抽象模型将CachedModelManager定义为管理器，然后将基本缓存功能扩展到模型及其子项。它允许您定义每次保存时应删除的volatile列表（因此是post_save信号），并添加一些辅助函数来生成缓存键，以及检索，设置和删除键。

This of course assumes you have a cache backend setup and working properly.

这当然假设您有一个缓存后端设置并正常工作。

# helperapp\models.py
# -*- coding: UTF-8
from django.db import models
from django.core.cache import cache

class CachedModelManager(models.Manager):
    def contribute_to_class(self, model, name):
        super(CachedModelManager, self).contribute_to_class(model, name)

        setattr(model, 'volatile_cache_keys',
                getattr(model, 'volatile_cache_keys', []))

        setattr(model, 'cache_key', getattr(model, 'cache_key', cache_key))
        setattr(model, 'get_cache', getattr(model, 'get_cache', get_cache))
        setattr(model, 'set_cache', getattr(model, 'set_cache', set_cache))
        setattr(model, 'del_cache', getattr(model, 'del_cache', del_cache))

        self._bind_flush_signal(model)

    def _bind_flush_signal(self, model):
        models.signals.post_save.connect(flush_volatile_keys, model)

def flush_volatile_keys(sender, **kwargs):
    instance = kwargs.pop('instance', False)

    for key in instance.volatile_cache_keys:
        instance.del_cache(key)

def cache_key(instance, key):
    if not instance.pk:
        name = "%s.%s" % (instance._meta.app_label, instance._meta.module_name)
        raise models.ObjectDoesNotExist("Can't generate a cache key for " +
                                        "this instance of '%s' " % name +
                                        "before defining a primary key.")
    else:
        return "%s.%s.%s.%s" % (instance._meta.app_label,
                                instance._meta.module_name,
                                instance.pk, key)

def get_cache(instance, key):
    result = cache.get(instance.cache_key(key))
    return result

def set_cache(instance, key, value, timeout=60*60*24*3):
    result = cache.set(instance.cache_key(key), value, timeout)
    return result

def del_cache(instance, key):
    result = cache.delete(instance.cache_key(key))
    return result


# myapp\models.py
from django.contrib.auth.models import User
from django.db import models

from helperapp.models import CachedModelManager

class Abstract(models.Model):
    creator = models.ForeignKey(User)

    cache = CachedModelManager()

    class Meta:
        abstract = True


class Community(Abstract):
    members = models.ManyToManyField(User)

    volatile_cache_keys = ['members_list',]

    @property
    def members_list(self):
        result = self.get_cache('members_list')

        if not result:
            result = self.members.all()
            self.set_cache('members_list', result)

        return result

Patches welcome!

补丁欢迎！

#1