Serializer Nested relationships not working as it sholuld be

Question

Nested relationships django 1.11

serializer:

class PostDetailSerializer(ModelSerializer):
    url = post_detail_url
    user = UserSerializer(read_only=True)
    image = SerializerMethodField()
    html = SerializerMethodField()
    tags = TagSerializer(many=True)
    category = CategorySerializer()
    source = SourceSerializer()

    class Meta:
        model = Post
        fields = [
            'id',
            'url',
            'title',
            'image',
            'slug',
            'content',
            'source',
            'source_link',
            'category',
            'tags',
            'html',
            'publish',
            'timestamp',
            'user',
        ]

Response:

HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Content-Type: application/json
Vary: Accept

{
    "id": 3,
    "url": "http://127.0.0.1:8000/api/v1/posts/new-postas/",
    "title": "New Postaas",
    "image": null,
    "slug": "new-postas",
    "content": "asssaasssasa",
    "source": {
    "id": 1,
    "name": "prothom alo",
    "slug": "prothom-alo"
    },
    "source_link": "http://prothom-alo.com/",
    "category": {
        "id": 2,
        "url": "http://127.0.0.1:8000/api/v1/posts/category/news/",
        "name": "news"
    },
    "tags": [
        {
            "id": 1,
            "name": "tech",
            "slug": "tech"
        }
    ],
    "html": "<p>asssaasssasa</p>\n",
    "publish": "2017-08-31",
    "timestamp": "2017-08-31T12:28:28.686538Z",
    "user": {
        "id": "ac32460f-fb7e-4755-9f7e-7c13085ee92b",
        "email": "[email protected]",
        "first_name": "Hasibul Amin",
        "last_name": "Hemel"
    }
}

This is fine nested relation retrieving the data.

But again in my category details api serializer below:

class CategoryDetailSerializer(ModelSerializer):
    url = category_detail_url
    posts = PostDetailSerializer(many=True, read_only=True)

    class Meta:
        model = Category
        fields = [
            'id',
            'url',
            'name',
            'posts'
        ]

Here my post serializer does not output any data in the api. I don't know. there no bug or error, just the value is not coming.

The category details api response:

HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Content-Type: application/json
Vary: Accept

{
    "id": 2,
    "url": "http://127.0.0.1:8000/api/v1/posts/category/news/",
    "name": "news"
}

Is there any solution? i searched but not found any.

Answer 1

Since you are using fieldname posts in CategoryDetailSerializer you need to set related_name=posts to category relation inside Post model:

class Post(Model):
    category = ForeignKey(Category, related_name='posts')

Or you can use default relation name post_set in CategoryDetailSerializer:

class CategoryDetailSerializer(ModelSerializer):
    url = category_detail_url
    post_set = PostDetailSerializer(many=True, read_only=True)

    class Meta:
        model = Category
        fields = [
        'id',
        'url',
        'name',
        'post_set'
        ]

See details here.

Also you can try to specify source on the serializer field using related_name from model:

posts = PostDetailSerializer(many=True, read_only=True, source='cat_posts')

Answer 2

I think that the CategoryDetailSerializer() not get called, What's get called is the other Category serializer who is the CategorySerializer().