django manytomanyfield .add（）方法 [英] django manytomanyfield .add() method

问题描述

假设我有：

class Album(models.Model):
    photos = models.ManyToManyField('myapp.Photo')
    photo_count = models.IntegerField(default = 0)

class Photo(models.Model):
    photo = models.ImageField(upload_to = 'blahblah')

想要的是，每次我调用.add（）方法，增加 photo_count on Album class，所以我正在考虑重写.add（）方法。问题是，我无法导入 .add（）的类，因为它在一个方法中，所以它像 def-> ;类 - > DEF 。那么有没有办法覆盖 .add（）？还是有更好的方法呢？

What is want is, everytime i call .add() method, increment the photo_count on Album class, so i'm thinking to override .add() method. The problem is, i can't import the .add()'s class since it is inside a method, so it is like def->class->def. So is there anyway to override .add() ? Or there is a better way to do this?

推荐答案

你可以使用django的信号并写一个信号处理程序，它将使用 m2m_changed 信号：

You can use django's signals and write a signal handler that will increment the counter using the m2m_changed signal:

https://docs.djangoproject.com/en/dev/ref/signals/#m2m-changed

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