django rest-farmework nested relationships to use filter

Question

Using django rest-farmework to implement the API,There is a problem has been unable to solve: How to filter the associated tables?, the specific code is as follows:

models.py

class Category(models.Model):
    name = models.CharField(max_length=30)
    amount = models.IntegerField()

class Source(models.Model):
    name = models.CharField(max_length=50)
    rss_link = models.URLField()
    amount = models.IntegerField()
    # ForeignKey
    category = models.ForeignKey(Category)

views.py

class CategoryListView(APIView):
    def get(self, request):
        category = Category.objects.all()
        serializers = CategorySerializers(category, many=True)
        return Response(serializers.data)

serializers.py

class SourceSerializers(serializers.ModelSerializer):
    class Meta:
        model = Source
        fields = ("id","name","amount")

class CategorySerializers(serializers.ModelSerializer):
    source_set = SourceSerializers(many=True, read_only=True)

    class Meta:
        model = Category
        fields = ("id","name","amount","source")

Program running results：

[
    {
        "id": 1,
        "name": "study",
        "amount": "0",
        "source": [
            {
                "id": 34,
                "name": "java",
                "amount": "0"
            },
            {
                "id": 35,
                "name": "python",
                "amount": "0"
            },
            {
                "id": 36,
                "name": "css",
                "amount": "2"
            }
        ]
    }
]

Now I only need to query "source" of the "amount" of 0 data, I tried to write this code:

serializers.py

class SourceSerializers(serializers.ModelSerializer):
    class Meta:
        model = Source
        fields = ("id","name","amount")

class CategorySerializers(serializers.ModelSerializer):

    #Modified the following code
    source_set = SourceSerializers(Source.objects.filter(amount=0),many=True, read_only=True)

    class Meta:
        model = Category
        fields = ("id","name","amount","source")

Modified the following code：

source_set = SourceSerializers(many=True, read_only=True)

to

source_set = SourceSerializers(Source.objects.filter(amount=0),many=True, read_only=True)

But the result is the same, I hope the result is:

[
    {
        "id": 1,
        "name": "study",
        "amount": "0",
        "source": [
            {
                "id": 34,
                "name": "java",
                "amount": "0"
            },
            {
                "id": 35,
                "name": "python",
                "amount": "0"
            }
        ]
    }
]

Thanks in advance.

Answer 1

You could use a SerializerMethodField:

class CategorySerializer(serializers.ModelSerializer):
    source_set = serializers.SerializerMethodField('get_sources')

    def get_sources(self, category):
        sources = category.source_set.filter(amount=0)
        return SourceSerializer(instance=sources, many=True).data

    class Meta:
        model = Category
        fields = ("id", "name", "amount", "source")

I removed the plural 's' from your class names because they were giving me an itch ;)

Answer 2

Change your Serializers a bit. You can have a SourceWithCategorySerializer that serializes the related Category object. Then, you are able to query Source objects based on amount and pass that QuerySet to your serializer.

Your view:

class CategoryListView(APIView):
    def get(self, request):
        sources = Source.objects.filter(amount=0)
        serializers = SourceWithCategorySerializers(sources, many=True)
        return Response(serializers.data)

The serializers:

class SourceWithCategorySerializers(serializers.ModelSerializer):
    category = CategorySerializer(read_only=True)

    class Meta:
        model = Source
        fields = ("id","name","amount", "category")

class CategorySerializers(serializers.ModelSerializer):
    class Meta:
        model = Category
        fields = ("id","name","amount")