Django Rest Framework 排序过滤器，按嵌套列表长度排序

Question

我通过settings.py 在全球范围内使用OrderingFilter，效果很好。

现在我想从ManyToManyField 订购嵌套列表的大小。使用默认的OrderingFilter 可以吗？

如果没有，有没有办法我可以使用自定义过滤器来做到这一点，同时将查询参数 ordering 保留在 url (http://example.com/recipes/?ordering=) 中。为了一致性。

哦，ManyToManyField 是一个直通表。

这些是我的models.py：

class Recipe(models.Model):
    name = models.CharField(max_length=255)
    cook_time = models.FloatField()
    ingredients = models.ManyToManyField(IngredientTag, through=Ingredient)

我的serializers.py：

class IngredientTagSerializer(serializers.ModelSerializer):
    class Meta:
        model = IngredientTag
        fields = ('id', 'label')

class IngredientSerializer(serializers.ModelSerializer):
    class Meta:
        model = Ingredient
        fields = ('amount', 'unit', 'ingredient_tag')
        depth = 1

class RecipeSerializer(serializers.ModelSerializer):
    ingredients = IngredientSerializer(source='ingredient_set', many=True)

    class Meta:
        model = Recipe
        fields = ('id', 'url', 'name', 'ingredients', 'cook_time')
        read_only_fields = ('owner',)
        depth = 2

还有我的views.py：

class RecipeViewSet(viewsets.ModelViewSet):
    """
    API endpoint that allows recipes to be viewed or edited.
    """
    queryset = Recipe.objects.all().order_by()
    serializer_class = RecipeSerializer
    permission_classes = (DRYPermissions,)
    ordering_fields = ('cook_time',) #Need ingredient count somewhere?

谢谢！

Answer 1

试试：

class RecipeSerializer(serializers.ModelSerializer):
    ingredients = IngredientSerializer(source='ingredient_set', many=True)
    ingredients_length = serializers.SerializerMethodField()

    class Meta:
        model = Recipe
        fields = ('id', 'url', 'name', 'ingredients', 'cook_time')
        read_only_fields = ('owner',)
        depth = 2

    def get_ingredients_length(self, obj):
        return obj.ingredients.count()

然后按成分长度排序

编辑

在model.py中，试试this:

@property
    def ingredient_length(self):
        return self.ingredient_set.count()