如何在DRF中访问ListSerializer父类上的serializer.data？ [英] How to access serializer.data on ListSerializer parent class in DRF?

问题描述

在访问 serializer.data 并在 Response（serializer.data，status = something）中返回之前，我遇到错误。 ：

尝试获取字段< field>的值时获取KeyError； 在序列化器< serializer> 上。

在所有字段上都会发生这种情况（因为事实证明我试图在父级而不是子级上访问 .data ，请参见下文）

This occurs on all fields (because it turns out I'm trying to access .data on the parent and not the child, see below)

类定义如下：

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 并具有重写的 save（）方法，该方法可以正确处理批量创建和更新。

CustomProductListSerializer is a serializers.ListSerializer and has an overridden save() method that allows it to correctly handle bulk create and update.

以下是批量产品 ViewSet 的示例视图：

Here's an example view from the bulk Product 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)

尝试访问<$跟踪中的c $ c> serializer.data （或后面的行）会导致错误。这是完整的跟踪记录（tl; dr跳过下面用调试器诊断的位置）：

Trying to access serializer.data at the trace (or the line after, obviously) causes the error. Here's the full trace (tl;dr skip below where I diagnose with debugger):

 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（此处的资源）我得到了：

At the L657 of the traceback (source here) I've got:

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（深入探究）为什么serializer.fields不可用。我怀疑这是因为序列化程序是 CustomProductListSerializer 的父级，而不是 BulkProductSerializer 的子级，我是对的。在返回 Response（serializer.data）之前的pdb跟踪中：

This made me wonder (digging further down in the trace) why the serializer.fields were not available. I suspected it was because the serializer was a CustomProductListSerializer parent, and not a BulkProductSerializer child, and I was right. In the pdb trace just before returning the 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)}

确定，那么获取完整的 serializer.data 并将其返回的正确方法是什么在我的 ViewSet 中的 partial_update 描述的情况下，对父序列化器类的响应？

OK, so what's the right way to get the complete serializer.data and return it in the resopnse for the parent serializer class in the situation described by partial_update in my 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

推荐答案

在跟踪中尝试访问 serializer.data 的位置KeyError，我注意到 serializer.data 仅包含 initial_data 中的键/值对，而不包含实例数据（因此，我想是KeyError；某些模型字段的键不存在，因为它是 partial_update 请求）。但是， serializer.child.data 确实包含列表中最后一个孩子的所有实例数据。

At the point in the trace where I try to access serializer.data and get the KeyError, I note that serializer.data only contains key/vaule pairs from the initial_data, not the instance data (hence, I suppose, the KeyError; some model fields' keys are not present as it is a partial_update request). However, serializer.child.data does contain all the instance data for the last child in the list.

因此，我转到 rest_framework / serializers.py 源其中定义了数据：

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。我可以通过调用 serializer.child.to_representation（{'uuid'：'87956604-fbcb-4244-bda3-9e39075d510a'，'product_code'：'foobar'}）复制该错误

Line 265 is problematic. I can replicate the error by calling serializer.child.to_representation({'uuid': '87956604-fbcb-4244-bda3-9e39075d510a', 'product_code': 'foobar'}) at the breakpoint.

在单个实例上调用 partial_update（）可以正常工作（因为<$ c $设置了c> self.instance ， 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，而 to_representation（）会'不能正常工作，因此我将无法访问 .data 属性。

Calling partial_update() works fine on a single instance (because self.instance is set, self.to_representation(self.instance) works). However, for a bulk partial_update() implementation, self.validated_data is missing model fields, and to_representation() won't work, so I won't be able to access the .data property.

一个选择是维护某种 self.instances 产品实例列表，并在第265行覆盖 data 的定义：

One option would be to maintain some sort of self.instances list of Product instances, and override the definition of data on line 265:

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

我真的希望有一个在这种问题上更有经验的人提供答案，因为我不确定这是否是一个明智的解决方案，因此我会悬赏希望有人可以提出更明智的建议。

I'd really prefer an answer from someone more experienced in this sort of problem though, as I'm not sure if that's a sensible solution, hence I'm leaving the bounty open in the hope that someone can suggest something smarter to do.

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