Django模式继承：创建现有实例的子实例（downcast）？

问题描述

我正在尝试整合一个第三方Django应用程序，这个应用程序使得不幸的决定继承自 django.contrib.auth.models.User ，这是一个很大的 - 不可插入的应用程序。引用：

I'm trying to integrate a 3rd party Django app that made the unfortunate decision to inherit from django.contrib.auth.models.User, which is a big no-no for pluggable apps. Quoting Malcolm Tredinnick:

嗯，我处于需要将此第三方应用程序与现有用户实例集成的情况。所以，如果假设我确实愿意在封面下捅，我的选择是什么？我知道这不行：

Well, I'm in the situation where I need to integrate this 3rd party app with my existing user instances. So, if hypothetically I am indeed willing to poke about under the covers, what are my options? I know that this doesn't work:

extended_user = ExtendedUser(user_ptr_id=auth_user.pk)
extended_user.save()

没有例外，但它打破了各种各样的东西，从覆盖所有的列开始 django.contrib.auth.models.User 与空字符串...

There's no exception, but it breaks all kinds of stuff, starting with overwriting all the columns from django.contrib.auth.models.User with empty strings...

推荐答案

这应该可以工作：

extended_user = ExtendedUser(user_ptr_id=auth_user.pk)
extended_user.__dict__.update(auth_user.__dict__)
extended_user.save()

这里你基本上只是复制超出从auth_user版本到extended_user的值，并重新保存。不是很优雅，但它的作品。

Here you're basically just copying over the values from the auth_user version into the extended_user one, and re-saving it. Not very elegant, but it works.

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