Question

我正在尝试创建自定义的ForeignKey。我继承了它并试图覆盖__init__方法以提供位置参数to和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makemigrations时，它会给我以下错误：

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

我似乎无法弄清问题是什么。我只为两个位置参数提供两个值。

Answer 1

假设您在所有者字段中传递User和on delete参数，您可以看到Django如何转换其参数。

实施例

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

正如您所看到的，Django正在将auth.User和models.CASCADE转换为分别包含密钥to和on_delete的字典。即，{'to': 'auth.User', 'on_delete': <function CASCADE at 0x103900400>}。

因此，在您的情况下，您应该为键to和on_delete设置默认值以获得预期的行为。

即，

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()

如何继承ForeignKey来扩展模型字段？

1 个答案: