DRF中ModelViewSet与函数视图返回ImageField结果不一致问题

我使用Django Rest Framework构建示例应用时，发现代表用户评分的Rating模型的ImageField字段，在ModelViewSet和基于函数的视图中返回结果不一致：

• ModelViewSet请求返回完整URL："photo": "http://127.0.0.1:8000/media/images/ratings/image.jpg"
• 函数视图请求仅返回相对路径："photo": "/media/images/ratings/image.jpg"

相关代码 #

Rating模型

class Rating(models.Model):
    
    user = models.ForeignKey(settings.AUTH_USER_MODEL,on_delete=models.CASCADE)
    rating = models.IntegerField()
    review = models.CharField(max_length=500)
    recipe = models.ForeignKey(Recipe,on_delete=models.CASCADE, related_name='ratings')
    published_date = models.DateField(default=date.today)
    updated_date = models.DateField(default=date.today)
    photo = models.ImageField(upload_to='images/ratings/', blank=True)

RatingViewSet代码

class RatingViewSet(viewsets.ModelViewSet):
    serializer_class = RatingSerializer
    lookup_fields = ('id', 'recipe')
    filter_backends = [DjangoFilterBackend]
    filterset_class = RatingFilter 

    queryset = Rating.objects.all()

    def perform_create(self, serializer):
        serializer.save(user=self.request.user)

    def perform_update(self, serializer):
        serializer.save(updated_date=date.today())

函数视图代码

@api_view(['GET'])
def UserRating(request):
    recipe_id = request.query_params.get('recipe_id')

    try:
        rating = Rating.objects.filter(recipe=recipe_id, user=request.user).latest('updated_date')
        serializer = RatingSerializer(rating)

        return Response(serializer.data, status=status.HTTP_200_OK)
    except Rating.DoesNotExist:
        return Response({})

原因 #

DRF的ModelViewSet会自动将当前请求的request对象传入序列化器的上下文（context）中，而序列化器的ImageField字段需要依赖这个上下文来生成包含域名、协议的完整绝对URL。

但在你的函数视图中，初始化RatingSerializer时没有手动传入request上下文，导致序列化器无法获取请求的域名信息，只能返回媒体文件的相对路径。

解决方案 #

在函数视图中初始化序列化器时，通过context参数传入当前request对象：

@api_view(['GET'])
def UserRating(request):
    recipe_id = request.query_params.get('recipe_id')

    try:
        rating = Rating.objects.filter(recipe=recipe_id, user=request.user).latest('updated_date')
        # 新增context参数传入request
        serializer = RatingSerializer(rating, context={'request': request})

        return Response(serializer.data, status=status.HTTP_200_OK)
    except Rating.DoesNotExist:
        return Response({})

这样修改后，函数视图返回的photo字段就会和ModelViewSet一样，生成完整的绝对URL。

内容的提问来源于stack exchange，提问作者Chowdahhh