Django REST Framework：如果相关字段不存在，则在 POST 上返回 404（而不是 400）？

我正在开发一个 REST API，它从一些无法修补或其他任何东西的真正脑死亡的软件中获取 POST 请求。 POST 用于更新数据库中已存在的模型对象。

具体来说，我正在发布具有相关字段（SlugRelatedField，因为 POSTer 知道“name”属性但不知道“pk”）的对象的数据。但是，如果 POSTer 发送的数据中“名称”在 SlugRelatedField 上没有返回任何内容（例如相关对象不存在），我需要返回 404。我已经使用调试器完成了这个任务，但似乎 DRF 使用了一些 Django 信号魔法来实现 DRF 的方式™，即返回 400 BAD REQUEST。我不知道如何修改这个 -only当它是上述条件并且不是真正的 400 值得 POST 时 - 变成 404。

顺便一提，pre_save()在我看来，在执行失败的测试期间不会执行。

这是序列化器：

class CharacterizationSerializer(serializers.ModelSerializer):
    """
    Work-in-progress for django-rest-framework use.  This handles (de)serialization
    of data into a Characterization object and vice versa.

    See: http://www.django-rest-framework.org/tutorial/1-serialization
    """
    creator = serializers.Field(source='owner.user.username')
    sample = serializers.SlugRelatedField(slug_field='name',
                                          required=True,
                                          many=False,
                                          read_only=False)

    class Meta:
        model = Characterization
        # leaving 'request' out because it's been decided to deprecate it. (...maybe?)
        fields = ('sample', 'date', 'creator', 'comments', 'star_volume', 'solvent_volume',
                  'solution_center', 'solution_var', 'solution_minimum', 'solution_min_stddev',
                  'solution_test_len',)

这是视图pre_save没有在给定的测试中运行（但在其他一些测试中运行）：

class CharacterizationList(generics.ListCreateAPIView):
    queryset = Characterization.objects.all()
    serializer_class = CharacterizationSerializer
    permission_classes = (AnonPostAllowed,)   # @todo XXX hack for braindead POSTer

    def pre_save(self, obj):
        # user isn't sent as part of the serialized representation,
        # but is instead a property of the incoming request.
        if not self.request.user.is_authenticated():
            obj.owner = get_dummy_proxyuser()   # this is done for CharacterizationList so unauthed users can POST. @todo XXX hack
        else:
            obj.owner = ProxyUser.objects.get(pk=self.request.user.pk)

        # here, we're fed a string sample name, but we need to look up
        # the actual sample model.
        # @TODO: Are we failing properly if it doesn't exist?  Should
        # throw 404, not 400 or 5xx.
        # except, this code doesn't seem to be run directly when debugging.
        # a 400 is thrown; DRF must be bombing out before pre_save?
        obj.sample = Sample.objects.get(name=self.request.DATA['sample'])

为了更好地衡量，这是失败的测试：

def test_bad_post_single_missing_sample(self):
    url = reverse(self._POST_ONE_VIEW_NAME)

    my_sample_postdict = self.dummy_plqy_postdict.copy()
    my_sample_postdict["sample"] = "I_DONT_EXIST_LUL"
    response = self.rest_client.post(url, my_sample_postdict)
    self.assertTrue(response.status_code == 404,
                    "Expected 404 status code, got %d (%s). Content: %s" % (response.status_code, response.reason_phrase, response.content))

如果我在self.rest_client.post()调用时，此时响应中已包含 400。

您可以使用 Django 快捷方式来获取 obj.sample：

from django.shortcuts import get_object_or_404
obj.sample = get_object_or_404(Sample, name=self.request.DATA['sample'])