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

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.

Answer 2

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.