Mixin Field 到现有且不可编辑的 django 模型中

发布于 2024-12-09 20:30:52 字数 880 浏览 1 评论 0原文

我想将一个字段混合到一个我不想编辑的现有模型中（它来自第三方项目，我宁愿让该项目保持不变）。我创建了一个简单的示例来说明我正在尝试但无法执行的操作：

在一个空的 Django 项目中，我创建了应用程序 app1 和 app2 （它们在设置中按该顺序排列）。它们看起来如下所示：

app1.models.py:

from django.db import models
from app2.models import BlogPost

class BlogPostExtend(models.Model):
    custom_field_name = models.CharField(max_length=200)

    class Meta:
        abstract = True

BlogPost.__bases__ = (BlogPostExtend,)+BlogPost.__bases__ # this prevents MRO error

app2.models.py:

from django.db import models

class BlogPost(models.Model):
    field_name = models.CharField(max_length=100)

不幸的是，当我syncdb时，这不会导致在数据库中创建custom_field_name，尽管在命令行中，如果我输入BlogPost.custom_field_name，它确实会将其识别为一个 CharField。我知道在这个简单的情况下，我可以让 BlogPost 继承自 BlogPostExtend，但在实际用例中，我无法编辑 BlogPost。

这是一个非常简单的例子，但它说明了我正在尝试做的事情。

谢谢！

原文

I would like to mix a field into an existing model which I would rather not edit (it comes from a third party project and I would rather leave the project untouched). I have created a simple example which illustrates what I am trying but unable to do:

In an empty Django project I have created apps app1 and app2 (they are in that order in settings). They look like the following:

app1.models.py:

from django.db import models
from app2.models import BlogPost

class BlogPostExtend(models.Model):
    custom_field_name = models.CharField(max_length=200)

    class Meta:
        abstract = True

BlogPost.__bases__ = (BlogPostExtend,)+BlogPost.__bases__ # this prevents MRO error

app2.models.py:

from django.db import models

class BlogPost(models.Model):
    field_name = models.CharField(max_length=100)

Unfortunately this does not result in custom_field_name being created in the database when I syncdb, although at the command line if I type BlogPost.custom_field_name it does recognize it as a CharField. I know that in this simple case I could have BlogPost inherit from BlogPostExtend, but in the real use case I cannot edit BlogPost.

This is a very simplified example but it illustrates what I am trying to do.

Thanks!

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人心善变 2024-12-16 20:30:52

Mixin 非常适合添加属性和方法，但不适用于字段。

在 app1.models.py 中，执行以下操作：

from django.db import models
from app2.models import BlogPost

custom_field_name = models.CharField(max_length=200)
custom_field_name.contribute_to_class(BlogPost, "custom_field_name")

我认为 app1 应用程序也应该位于 INSTALLED_APPS 中的 app2 之后> 使其发挥作用。

这是关于 contribute_to_class 的解释

Mixins work great with adding attributes and methods, but not fields.

In app1.models.py, do this instead:

from django.db import models
from app2.models import BlogPost

custom_field_name = models.CharField(max_length=200)
custom_field_name.contribute_to_class(BlogPost, "custom_field_name")

I think also the app1 app should come after app2 in INSTALLED_APPS for this to work.

Here is an explanation on contribute_to_class

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