Retrieving a Foreign Key value with django-rest-framework serializers

In the DRF version 3.6.3 this worked for me

class ItemSerializer(serializers.ModelSerializer):
    category_name = serializers.CharField(source="category.name")

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

More info can be found here: Serializer Fields core arguments