python - 如何在 DRF 中访问 ListSerializer 父类的 serializer.data？

Question

我在尝试访问 serializer.data 时遇到错误在 Response(serializer.data, status=something) 返回之前:

Getting KeyError when attempting to get a value for field <field> on serializer <serializer>.

这发生在所有字段上(因为事实证明我正在尝试访问父而不是子上的 .data，见下文)

类定义如下所示:

class BulkProductSerializer(serializers.ModelSerializer):

    list_serializer_class = CustomProductListSerializer

    user = serializers.CharField(source='fk_user.username', read_only=False)

    class Meta:
        model = Product
        fields = (
            'user',
            'uuid',
            'product_code',
            ...,
        )

CustomProductListSerializer是 serializers.ListSerializer并且有一个被覆盖的 save()允许它正确处理批量创建和更新的方法。

这是批量产品 ViewSet 的示例 View :

def partial_update(self, request):

    serializer = self.get_serializer(data=request.data,
                        many=isinstance(request.data, list),
                        partial=True)
    if not serializer.is_valid():
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
    serializer.save()
    pdb.set_trace()
    return Response(serializer.data, status=status.HTTP_200_OK)

正在尝试访问 serializer.data在跟踪处(或之后的行，显然)会导致错误。这是完整的跟踪(tl;dr 跳过下面我用调试器诊断的地方):

 Traceback (most recent call last):
  File "/lib/python3.5/site-packages/django/core/handlers/exception.py", line 41, in inner
    response = get_response(request)
  File "/lib/python3.5/site-packages/django/core/handlers/base.py", line 249, in _legacy_get_response
    response = self._get_response(request)
  File "/lib/python3.5/site-packages/django/core/handlers/base.py", line 187, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/lib/python3.5/site-packages/django/core/handlers/base.py", line 185, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/lib/python3.5/site-packages/django/views/decorators/csrf.py", line 58, in wrapped_view
    return view_func(*args, **kwargs)
  File "/lib/python3.5/site-packages/rest_framework/viewsets.py", line 86, in view
    return self.dispatch(request, *args, **kwargs)
  File "/lib/python3.5/site-packages/rest_framework/views.py", line 489, in dispatch
    response = self.handle_exception(exc)
  File "/lib/python3.5/site-packages/rest_framework/views.py", line 449, in handle_exception
    self.raise_uncaught_exception(exc)
  File "/lib/python3.5/site-packages/rest_framework/views.py", line 486, in dispatch
    response = handler(request, *args, **kwargs)
  File "/application/siop/views/API/product.py", line 184, in partial_update
    return Response(serializer.data, status=status.HTTP_200_OK)
  File "/lib/python3.5/site-packages/rest_framework/serializers.py", line 739, in data
    ret = super(ListSerializer, self).data
  File "/lib/python3.5/site-packages/rest_framework/serializers.py", line 265, in data
    self._data = self.to_representation(self.validated_data)
  File "/lib/python3.5/site-packages/rest_framework/serializers.py", line 657, in to_representation
    self.child.to_representation(item) for item in iterable
  File "/lib/python3.5/site-packages/rest_framework/serializers.py", line 657, in <listcomp>
    self.child.to_representation(item) for item in iterable
  File "/lib/python3.5/site-packages/rest_framework/serializers.py", line 488, in to_representation
    attribute = field.get_attribute(instance)
  File "/lib/python3.5/site-packages/rest_framework/fields.py", line 464, in get_attribute
    raise type(exc)(msg)
KeyError: "Got KeyError when attempting to get a value for field `user` on serializer `BulkProductSerializer`.\nThe serializer field might be named incorrectly and not match any attribute or key on the `OrderedDict` instance.\nOriginal exception text was: 'fk_user'."

在回溯的 L657(source here) 我有:

iterable = data.all() if isinstance(data, models.Manager) else data
return [
    self.child.to_representation(item) for item in iterable
]

这让我想知道(在跟踪中进一步挖掘)为什么 serializer.fields 不可用。我怀疑这是因为序列化程序是 CustomProductListSerializer parent ，而不是 BulkProductSerializer child ，我是对的。在返回 Response(serializer.data) 之前的 pdb 跟踪中:

(Pdb) serializer.fields
*** AttributeError: 'CustomProductListSerializer' object has no attribute 'fields'
(Pdb) serializer.child.fields
{'uuid': UUIDField(read_only=False, required=False, validators=[]) ...(etc)}
(Pdb) 'user' in serializer.child.fields
True
(Pdb) serializer.data
*** KeyError: "Got KeyError when attempting to get a value for field `user` on serializer `BulkProductSerializer`.\nThe serializer field might be named incorrectly and not match any attribute or key on the `OrderedDict` instance.\nOriginal exception text was: 'fk_user'."
(Pdb) serializer.child.data
{'uuid': '08ec13c0-ab6c-45d4-89ab-400019874c63', ...(etc)}

好的，那么获得完整 serializer.data 的正确方法是什么？并在 partial_update 描述的情况下在父序列化程序类的响应中返回它在我的 ViewSet ？

编辑:

class CustomProductListSerializer(serializers.ListSerializer):

    def save(self):
        instances = []
        result = []
        pdb.set_trace()
        for obj in self.validated_data:
            uuid = obj.get('uuid', None)
            if uuid:
                instance = get_object_or_404(Product, uuid=uuid)
                # Specify which fields to update, otherwise save() tries to SQL SET all fields.
                # Gotcha: remove the primary key, because update_fields will throw exception.
                # see https://stackoverflow.com/a/45494046
                update_fields = [k for k,v in obj.items() if k != 'uuid']
                for k, v in obj.items():
                    if k != 'uuid':
                        setattr(instance, k, v)
                instance.save(update_fields=update_fields)
                result.append(instance)
            else:
                instances.append(Product(**obj))

        if len(instances) > 0:
            Product.objects.bulk_create(instances)
            result += instances

        return result

Answer 1

如评论中所述，我仍然认为异常可能是因为 BulkProductSerializer 类中的用户字段，与 ListSerializer

没有任何关系

序列化程序 DRF 中可能存在另一个小错误(但很重要)，如文档中所述 here .以下是指定 list_serializer_class 的方法:

class CustomListSerializer(serializers.ListSerializer):
    ...

class CustomSerializer(serializers.Serializer):
    ...
    class Meta:
        list_serializer_class = CustomListSerializer

请注意，它是在 Meta 类内部指定的，而不是在外部指定的。所以我认为在您的代码中，使用 many=True 切换到 List Serializer 将无法理解。那应该会导致不更新的问题。

更新 - 添加更新嵌套列表序列化程序的示例

问题似乎更多地是关于实现嵌套列表序列化器更新的通用方法，而不是实际错误。因此，我将尝试提供示例代码。

一些注意事项:

• 如果我们使用ModelViewSet，列表路由将不允许PUT 或PATCH，所以更新 partial_update 也不会被调用 ( reference )。所以我直接使用POST，这样就简单多了。
• 如果您想使用PUT/PATCH，请查看此答案here
• 我们总是可以直接向 Post 请求添加一个查询参数，例如 allow_update 或 partial 以区分 POST/PUT/PATCH
• 我不会像问题那样使用uuid，而是使用普通的id，它应该非常相同

比较简单

供引用，模型如下所示:

class Product(models.Model):
    name = models.CharField(max_length=200)
    user = models.ForeignKey(User, null=True, blank=True)

    def __unicode__(self):
        return self.name

第 1 步:确保序列化程序更改为 ListSerializer

class ProductViewSet(viewsets.ModelViewSet):
    serializer_class = ProductSerializer
    queryset = Product.objects.all()

    def get_serializer(self, *args, **kwargs):
        # checking for post only so that 'get' won't be affected
        if self.request.method.lower() == 'post':
            data = kwargs.get('data')
            kwargs['many'] = isinstance(data, list)
        return super(ProductViewSet, self).get_serializer(*args, **kwargs)

第 2 步:通过重写 create 函数实现 ListSerializer

class ProductListSerializer(serializers.ListSerializer):
    def create(self, validated_data):
        new_products = [Product(**p) for p in validated_data if not p.get('id')]
        updating_data = {p.get('id'): p for p in validated_data if p.get('id')}
        # query old products
        old_products = Product.objects.filter(id__in=updating_data.keys())
        with transaction.atomic():
            # create new products
            all_products = Product.objects.bulk_create(new_products)
            # update old products
            for p in old_products:
                data = updating_data.get(p.id, {})
                # pop id to remove
                data.pop('id')
                updated_p = Product(id=p.id, **data)
                updated_p.save()
                all_products.append(updated_p)
        return all_products


class ProductSerializer(serializers.ModelSerializer):
    user = serializers.SlugRelatedField(slug_field='username', queryset=User.objects.all())
    id = serializers.IntegerField(required=False)

    class Meta:
        model = Product
        fields = '__all__'
        list_serializer_class = ProductListSerializer