Django rest framework - filtering for serializer field

How about something like this:

class ProductSerializer(serializers.ModelSerializer):
    likes = serializers.SerializerMethodField()

    def get_likes(self, product):
        qs = Like.objects.filter(whether_like=True, product=product)
        serializer = LikeSerializer(instance=qs, many=True)
        return serializer.data

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

**LikeSerializer omitted for brevity. Hope this helps.

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.