删除用作外键的对象 [英] Deletion objects that is used as foreign key

问题描述

我有下一个模型：

class Target(models.Model):
    name = models.CharField(max_length=100, blank=False)


class SubTarget(models.Model):
    target = models.ForeignKey(Target, related_name='sub_targets')
    name = models.CharField(max_length=100, blank=True, null=True, default='')

例如，我运行下一个代码：

For example, I run next code:

target = Target(name='test-target')
target.save()
sub_target = SubTarget(name='test-sub-target, target=target)
sub_target.save()

所以现在我有一个带外键的sub_target对象。

So now I have sub_target object with foreign key.

我的目标序列化器如下所示：

My serializer for target looks like:

class TargetSerializer(serializers.ModelSerializer):
    class Meta:
        model = Target
        fields = ('id', 'name', 'sub_targets')
        depth = 1
        read_only_fields = ('sub_targets',)

和适当的视图：

class TargetDetail(generics.RetrieveUpdateDestroyAPIView):
    model = Target
    serializer_class = TargetSerializer

所以，没有什么可以阻止我删除只是使用外键 target 创建的对象。而且，此操作也删除相关的 sub_target 对象。如何避免这种行为？

So, nothing prevents me from deletion just target created object with foreign key. Moreover, this operation delete also related sub_target object. How can I avoid this behaviour ?

推荐答案

我不知道，但是我想你在询问如何在删除目标时防止SubTarget对象被删除对象。默认情况下，Django模拟ON DELETE CASCADE。您可以使用on_delete关键字来控制此行为。

I'm not sure, but I think you're asking how to prevent SubTarget objects from being deleted when you delete Target objects. By default Django emulates ON DELETE CASCADE. You can control this behavior with the on_delete key word.

所以：

class Target(models.Model):
    name = models.CharField(max_length=100, blank=False)


class SubTarget(models.Model):
    target = models.ForeignKey(Target, related_name='sub_targets', 
                               null=True, on_delete=models.SET_NULL)
    name = models.CharField(max_length=100, blank=True, null=True, default='')

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