删除用作外键的对象

Question

我有下一个型号：

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：

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

所以现在我有了带外键的sub_target对象。

我的目标序列化器看起来像：

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用外键创建目标。而且，此操作删除了相关的sub_target对象。我该如何避免这种行为？

Answer 1

我不确定，但我想你在询问如何在删除Target对象时阻止删除SubTarget对象。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

在寻找一种方法来检查是否可以在django中删除模型实例之后，我遇到了很多样本​​，但是没有按预期工作。希望这个解决方案有所帮助

首先创建一个可以由其他模型继承的抽象模型类

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

Example

因此，假设我们有三个模型组织和部门以及StaffType这么多部门可以在一个组织中并且一个组织具有特定的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，在添加一些信息之后，您要删除已绑定到部门的组织模型实例

例如，我们有Organization Table =>（name = Engineering，pk = 1）Department Table =>（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

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

有了这个，你可以检查它是否可删除

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 3

也许你可以尝试另一种方式，我只是用我的项目，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 4

延迟回复，但也可以使用ForeignKey上的model.PROTECT来避免

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 5

您可以覆盖模型的删除操作，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没有反向关系，则它不起作用。