删除用作外键的对象

Question

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，我运行下一段代码：

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

所以现在我有了带有外键的 sub_target 对象。

我的目标序列化器如下所示：

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

和适当的观点：

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

所以，没有什么能阻止我删除只是 target 使用外键创建的对象。而且，这个操作还删除了相关的sub_target对象。我怎样才能避免这种行为？

Answer 1

我不确定，但我认为您在问如何在删除 Target 对象时防止 SubTarget 对象被删除。默认情况下，Django 模拟 ON DELETE CASCADE。您可以使用 on_delete 关键字控制此行为。

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='')

Documentation

Answer 2

延迟回复，但也可以在 ForeignKey 上使用 model.PROTECT 来避免这种情况

target = models.ForeignKey( Target, related_name='sub_targets', on_delete=models.PROTECT )

class BaseModel(models.Model):

    def can_delete(self):
        # get all the related object to be deleted
        for related in get_candidate_relations_to_delete(self._meta):
            field = related.field
            if field.remote_field.on_delete == models.PROTECT:
                # check for relationship with at least one related object
                related = related.related_model.objects.filter(**{related.field.name: self})
                if related.exists():
                    return False, related
        return True, None

    class Meta:
        abstract = True

Answer 3

在寻找一种方法来检查是否可以在 django 中删除模型实例后，我遇到了许多示例，但没有按预期工作。希望这个解决方案能有所帮助。

让我们从创建一个可以被其他模型继承的抽象模型类开始

class ModelIsDeletable(models.Model):
    name = models.CharField(max_length=200, blank=True, null=True, unique=True)
    description = models.CharField(max_length=200, blank=True, null=True)
    date_modified = models.DateTimeField(auto_now_add=True)

    def is_deletable(self):
        # get all the related object
        for rel in self._meta.get_fields():
            try:
                # check if there is a relationship with at least one related object
                related = rel.related_model.objects.filter(**{rel.field.name: self})
                if related.exists():
                    # if there is return a Tuple of flag = False the related_model object
                    return False, related
            except AttributeError:  # an attribute error for field occurs when checking for AutoField
                pass  # just pass as we dont need to check for AutoField
        return True, None

     class Meta:
        abstract = True

示例

假设我们有三个模型 Organization and Department 和 StaffType 一个组织中可以有这么多部门 并且一个组织有一个特定的 StaffType

class StaffType(ModelIsDeletable):
    pensionable = models.BooleanField(default=False)

class Organization(ModelIsDeletable):
    staff_type = models.ForeignKey(to=StaffType)


class Department(ModelIsDeletable):
    organization = models.ForeignKey(to=Organization, to_field="id")

所以在添加一些信息后说你想删除一个组织模型实例 已经绑定到一个部门

例如我们有 组织表 =>（名称 = 工程，pk = 1） 部门表 => (name=Developer, organization_fk=1, pk=1)

现在，当您尝试使用 pk 获取组织后删除组织时

a_org = Organization.objects.get(pk=1)

有了这个，你可以检查它是否可以删除

deletable, related_obj = a_org.is_deletable()

if not deletable:
    # do some stuff with the related_obj list

else:
    # call the delete function
    a_org.delete()

Answer 4

也许你可以尝试另一种方式，我刚刚为我的项目得到它，使用 Django 1.8

instance = get_object_or_404(MyModel, pk=pk)
eliminate = True
for robject in instance._meta.get_all_related_objects():
    if robject is not None:
        if robject.related_model.objects.filter(**{robject.field.name: instance}).exists() and eliminate:
            eliminate = False

if eliminate:
    instance.delete()
    # additional code
else:
    # additional code
    pass

Answer 5

您可以覆盖模型的删除操作，例如：

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

    def delete(self, *args, **kwargs):

        for robject in self._meta.get_all_related_objects():
            if robject is not None:
                q = Q(**{"%s__id" % robject.field.name: self.id})
                if robject.model.objects.filter(q).exists():
                    raise Exception("Item has active reference.")

        try:
            with transaction.atomic():
                super(Target, self).delete(*args, **kwargs)
        except Exception, exp:
            raise exp

请注意，如果相关对象与另一个对象没有反向关系，则它不起作用。