如何在DRF中的ListSerializer父类上访问serializer.data？

Question

我在尝试访问serializer.data之前遇到错误,然后返回Response(serializer.data, status=something):

尝试获取<field>序列化程序字段的值时获取KeyError <serializer>.

这发生在所有字段上(因为事实证明我试图访问.data父节点而不是子节点,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是一个serializers.ListSerializer有一个重写的save()方法,允许它正确处理批量创建和更新.

以下是批量产品的示例视图ViewSet:

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)

试图访问serializer.data跟踪(或明显后面的行)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'."

在追溯的L657(来源这里),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(在追踪中进一步挖掘)为什么serializer.fields不可用.我怀疑这是因为序列化器是CustomProductListSerializer父母,而不是BulkProductSerializer孩子,我是对的.在返回之前的pdb跟踪中Response(serializer.data):

(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,那么在我serializer.data所描述的情况下,获取完整并将其返回到父序列化程序类的resopnse中的正确方法是什么？partial_updateViewSet

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

正如评论中提到的,我仍然认为异常可能是因为BulkProductSerializer类中的用户字段,并不是真的与ListSerializer

如文档中提到的有可能是在串行DRF另一个小错误(但很重要)这里.以下是如何指定list_serializer_class:

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.所以我认为在你的代码中,切换到List Serializer并不明白many=True.这应该导致不更新的问题.

更新 - 添加更新嵌套列表序列化程序的示例

似乎问题更多的是关于实现嵌套List Serializer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.

一些说明:

• 如果我们使用ModelViewSet,列表路由将不允许PUT或PATCH,因此不会调用update或partial_update(引用).因此我直接使用POST,这更简单.
• 如果您想使用PUT/PATCH,请在此处查看此答案
• 我们总是可以将一个查询参数(如allow_update或partial)直接添加到Post请求中,以区分POST/PUT/PATCH
• 而不是像我将使用普通id这样的问题使用uuid,它应该是非常相同的

这很简单

作为参考,模型看起来像这样:

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:通过覆盖create function 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

Answer 2

在跟踪中我尝试访问serializer.data并获取 KeyError 的地方，我注意到serializer.data仅包含来自 的键/值对initial_data，而不包含实例数据（因此，我认为是 KeyError；某些模型字段的键不存在为这是一个partial_update请求）。但是，serializer.child.data确实包含列表中最后一个子项的所有实例数据。

因此，我转到定义的rest_framework/serializers.py源代码data：

249    @property
250    def data(self):
251        if hasattr(self, 'initial_data') and not hasattr(self, '_validated_data'):
252            msg = (
253                'When a serializer is passed a `data` keyword argument you '
254                'must call `.is_valid()` before attempting to access the '
255                'serialized `.data` representation.\n'
256                'You should either call `.is_valid()` first, '
257                'or access `.initial_data` instead.'
258            )
259            raise AssertionError(msg)
260
261        if not hasattr(self, '_data'):
262            if self.instance is not None and not getattr(self, '_errors', None):
263                self._data = self.to_representation(self.instance)
264            elif hasattr(self, '_validated_data') and not getattr(self, '_errors', None):
265                self._data = self.to_representation(self.validated_data)
266            else:
267                self._data = self.get_initial()
268        return self._data

第 265 行有问题。serializer.child.to_representation({'uuid': '87956604-fbcb-4244-bda3-9e39075d510a', 'product_code': 'foobar'})我可以通过在断点处调用来复制错误。

调用partial_update()在单个实例上工作正常（因为self.instance已设置，所以self.to_representation(self.instance)有效）。但是，对于批量partial_update() 实现，self.validated_data缺少模型字段，并且to_representation()无法工作，因此我将无法访问该.data属性。

一种选择是维护某种Product 实例列表，并覆盖第 265 行self.instances的定义：data

self._data = self.to_representation(self.instances)

不过，我真的更希望来自对此类问题更有经验的人的回答，因为我不确定这是否是一个明智的解决方案，因此我将悬赏开放，希望有人可以建议一些更聪明的事情。