Django rest framework - filtering for serializer field

Question

I have question about Django REST-full framework.

When products have rendered into remote client, each of product takes a filed with filtered data.

For example, model may be like this.

 class Product(models.Model):
      name = models.CharField()

 class Like(models.Model):
      product = models.ForeignKey(Product, related_name="likes")

On the client, each likes of product counted with true value, not false.

So I tried with below code in the serializer.

class ProductSerializer(serializers.ModelSerializer):

    likes = serializers.PrimaryKeyRelatedField(many=True, queryset=Like.objects.filter(whether_like=True))

    class Meta:
        model = Product
        fields = ('id', 'name', 'likes')

But, that is not working as I wanted.

What should I do?

The following is extra view code.

@api_view(['GET'])
def product_list(request, user_id, format=None):

    if request.method == 'GET':
        products = Product.objects.all()
        serializer = ProductSerializer(products, many=True)

        return Response(serializer.data)

Answer 1

Instead of SerializerMethodField, which causes one additional database query per object, you can now (starting with Django 1.7) use Prefetch objects in the queryset of your DRF ViewSet:

from rest_framework import viewsets
from django.db.models import Prefetch

class ProductViewSet(viewsets.ModelViewSet):
    queryset = Product.objects.prefetch_related(Prefetch(
        'likes',
        queryset=Like.objects.filter(like=True)))

The prefetch needs just one query, ensuring vastly superior performance compared to SerializerMethodField.