Django 外键 on_delete : how to pass argument to callable when using models. SET

Question

这是我的 models.py:

def set_image(instance):
    return Image.objects.filter(user=instance.user)[0]

class User(models.Model):
    user = models.CharField(max_length=50)

class Image(models.Model):
    user = models.ForeignKey(User)
    image = models.ImageField(upload_to='media')

class Item(models.Model):
    user = models.ForeignKey(User)
    image = models.ForeignKey(
        Image,
        blank=True,
        null=True,
        on_delete=models.SET(set_image)
    )

当我删除“图像”时，它与“项目”调用 set_image 相关，这会返回错误，因为 models.SET 不会将实例传递给可调用对象。我怎样才能改变这种行为？我应该覆盖 models.SET 还是有其他方法可以解决它？

Answer 1

重写 Image 删除方法以删除 ItemforeignKey

以下内容可以用作中间模型基类，将此功能添加到您的所有模型中:

from django.db import models

class Model(models.Model):
    """
    Intermediate model base class.
    """
    class Meta:
        abstract = True

    def delete(self, *args, **kwargs):
        self.clear_nullable_related()
        super(Model, self).delete(*args, **kwargs)

    def clear_nullable_related(self):
        """
        Recursively clears any nullable foreign key fields on related objects.
        Django is hard-wired for cascading deletes, which is very dangerous for
        us. This simulates ON DELETE SET NULL behavior manually.
        """
        for related in self._meta.get_all_related_objects():
            accessor = related.get_accessor_name()
            related_set = getattr(self, accessor)

            if related.field.null:
                related_set.clear()
            else:
                for related_object in related_set.all():
                    related_object.clear_nullable_related()

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