class ItemSerializer(serializers.ModelSerializer):
  class Meta:
    model = Item
    list_fields = ('id', 'name')
    detailed_fields = ('id', 'name', 'long_column')

from rest_framework.serializers import ModelSerializer
from rest_framework.viewsets import ModelViewSet

class ItemListSerializer(ModelSerializer):
    class Meta:
        model = Item
        fields = ('id', 'name')


class ItemDetailSerializer(ModelSerializer):
    class Meta:
        model = Item
        fields = ('id', 'name', 'long_column')


class ItemViewSet(ModelViewSet):
    queryset = Item.objects.all()
    serializer_class = ItemListSerializer

    def retrieve(self, request, *args, **kwargs):
        self.serializer_class = ItemDetailSerializer
        return super(ItemViewSet, self).retrieve(request, *args, **kwargs)