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

Question

我正在开发一个REST API，这个API需要处理一些非常简单的软件发来的POST请求，这些软件无法使用PATCH或者其他方法。这个POST请求是用来更新数据库中已经存在的模型对象。

具体来说，我在发送一些数据，这些数据是与某个字段相关的（一个叫做SlugRelatedField的字段，因为发送数据的人知道'名称'属性，但不知道'主键'）。不过，如果发送数据的人提供的'名称'在SlugRelatedField中找不到对应的对象，我需要返回一个404错误（也就是找不到的意思）。我用调试工具检查过，发现DRF（Django REST Framework）使用了一些Django的信号机制来处理这个问题，结果是返回了一个400错误（错误的请求）。我不知道怎么修改这个逻辑，让它在上述情况下返回404，而不是错误的400。

顺便提一下，我在我的视图中的pre_save()方法在测试失败时并没有被执行。

这是序列化器的代码：

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',)

这是视图的代码，在这个测试中pre_save没有被执行（但在其他一些测试中是会执行的）：

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'])

为了确保，我还附上了失败的测试代码：

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()调用处设置一个断点，到那时响应已经显示400错误了。

django database update error handling rest api http status codes serializer view logic slugrelatedfield

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

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