如何继承ForeignKey来扩展模型字段？

Question

我正在尝试创建一个自定义外键。我继承了它并尝试重写__init__方法来提供位置参数to，on_delete如下所示：

from django.contrib.auth.models import User

class CurrentUserField(models.ForeignKey):
    def __init__(self, **kwargs):
        super().__init__(User, models.CASCADE, **kwargs)


class DemoModel(models.Model):
    owner = CurrentUserField()
    info = models.TextField()

当我运行时它给我以下错误makemigrations：

TypeError: __init__() got multiple values for argument 'on_delete'

我似乎无法弄清楚问题是什么。我只为两个位置参数提供两个值。

Answer 1

假设如果您在所有者字段本身中传递User和参数，您可以看到 Django 如何转换其参数。on delete

例子

from django.db import models
from django.contrib.auth.models import User


class CurrentUserField(models.ForeignKey):
    def __init__(self, *args, **kwargs):
        for i in args:
            print(i, "This is an argument")

        for j in kwargs.items():
            print(j, "This is a keyword argument")
        super().__init__(*args, **kwargs)


class DemoModel(models.Model):
    owner = CurrentUserField(User, on_delete=models.CASCADE)
    info = models.TextField()

输出

<class 'django.contrib.auth.models.User'> This is an argument
('on_delete', <function CASCADE at 0x103900400>) This is a keyword argument
('on_delete', <function CASCADE at 0x103900400>) This is a keyword argument
('to', 'auth.User') This is a keyword argument
('on_delete', <function CASCADE at 0x103900400>) This is a keyword argument
('to', 'auth.User') This is a keyword argument

正如你所看到的，Django 正在将auth.User和分别转换为带有键和 的models.CASCADE字典。IE，。toon_delete{'to': 'auth.User', 'on_delete': <function CASCADE at 0x103900400>}

因此，在您的情况下，您应该设置键的默认值to并on_delete获得预期的行为。

IE，

from django.db import models
from django.contrib.auth.models import User


class CurrentUserField(models.ForeignKey):
    def __init__(self, *args, **kwargs):
        kwargs.setdefault('to', User)
        kwargs.setdefault('on_delete', models.CASCADE)
        super().__init__(*args, **kwargs)


class DemoModel(models.Model):
    owner = CurrentUserField()
    info = models.TextField()