TPT3 - adding dehydrate method

api.py

class TodoListResource(ModelResource):
    def dehydrate(self, bundle):
        items = bundle.obj.items.all()
        bundle.data['item_count'] = items.count()
        bundle.data['items'] = [i.to_dict() for i in items]

        return bundle

    class Meta:
        authentication = SessionAuthentication()
        authorization = AuthorizationByUser()
        queryset = TodoList.objects.all()
        resource_name = 'list'