unique_together 不允许更新记录

Question

我正在通过 Django Rest Framework 在移动应用程序 API 中实现 Like/Unlike 功能。

所以我有以下模型：

class PlaylistLikes(models.Model):
    user = models.ForeignKey(User)
    playlist = models.ForeignKey(Playlist)
    like = models.BooleanField(default=0, blank=True)

    class Meta:
        unique_together = ('user', 'playlist',)
        verbose_name = "Playlist like"
        verbose_name_plural = "Playlist likes"

我添加了unique_together 以限制用户喜欢他已经喜欢的播放列表。

我的看法：

class LikesView(viewsets.ModelViewSet):
    queryset = PlaylistLikes.objects.all()
    serializer_class = LikesSerializer
    filter_backends = (filters.OrderingFilter, filters.DjangoFilterBackend, filters.SearchFilter)
    filter_class = LikesFilter

    search_fields = ('playlist', 'user',)

    def create(self, request, *args, **kwargs):
        user = request.user
        request.data['user'] = user.pk
        serializer = self.get_serializer(data=request.data)
        serializer.is_valid(raise_exception=True)
        self.perform_create(serializer)
        return Response(serializer.data, status=status.HTTP_201_CREATED)

    @detail_route(methods=['put'])
    def put(self, request, *args, **kwargs):
        user = request.user
        request.data['user'] = user.pk
        serializer = self.get_serializer(data=request.data)
        serializer.is_valid(raise_exception=True)
        self.perform_update(serializer)
        return Response(serializer.data, status=status.HTTP_200_OK)

和序列化器：

class LikesSerializer(serializers.ModelSerializer):

    def create(self, validated_data):
        like = PlaylistLikes.objects.create(**validated_data)
        playlist = Playlist.objects.get(pk=like.playlist.id)
        playlist.likes_count += 1
        playlist.save()
        return validated_data

    def update(self, instance, validated_data):
        like = PlaylistLikes.objects.get(**validated_data)
        like.like = False
        like.save()
        playlist = Playlist.objects.get(pk=like.playlist.id)
        playlist.likes_count -= 1
        playlist.save()
        return validated_data

    class Meta:
        model = PlaylistLikes
        fields = ('user', 'playlist', 'like')

网址：

router.register(r'likes', views.LikesView, 'likes')

为喜欢播放列表，我发送POST 方法和正文playlist = 19，user = 3，like = 1。 Like 已成功创建。 与相同的播放列表不同，我发送 PUT 方法，正文为：playlist = 19，user = 3，但出现以下错误：

“non_field_errors”：[ “字段用户，播放列表必须设置唯一。” ]

我知道这是因为模型中的unique_together 而发生的。但我没有创建具有相同user 和playlist 的新记录。我只想更新现有记录。为什么会发生这种情况以及如何解决这个问题？

Answer 1

这是因为在 PUT 方法处理程序中，您创建了一个序列化程序而不指定实例：

serializer = self.get_serializer(data=request.data)

看Serializer.__init__()：

def __init__(self, instance=None, data=empty, **kwargs):
    self.instance = instance
    if data is not empty:
        self.initial_data = data
    self.partial = kwargs.pop('partial', False)
    self._context = kwargs.pop('context', {})
    kwargs.pop('many', None)
    super(BaseSerializer, self).__init__(**kwargs)

您没有提供实例参数，它默认为无。

对于更新，应跳过 unique_together 验证，仅当实例属性不是 None 时：

class UniqueTogetherValidator(object):
    def exclude_current_instance(self, attrs, queryset):
        """
        If an instance is being updated, then do not include
        that instance itself as a uniqueness conflict.
        """
        if self.instance is not None:
            return queryset.exclude(pk=self.instance.pk)
        return queryset

为了解决这个问题，可以在初始化序列化器之前移动Userlikes对象的查询：

like = PlaylistLikes.objects.get(**query)
serializer = self.get_serializer(like, data=request.data)