Views

Now it’s time to make our data visible to the outside world.

django-nap builds on Django’s Class-Based Generic Views.

Question List

Now it’s time to add our question list endpoint.

First, we’ll define a common QuestionMixin class to help hold common definitions for list and object views:

polls/views.py
 from nap.rest import views

 from . import mappers, models

 class QuestionMixin:
     model = models.Question
     mapper_class = mappers.QuestionMapper

Next we’ll define our QuestionListView, based on this and the BaseListView fron nap:

polls/views.py
 class QuestionListView(QuestionMixin,
                        views.BaseListView):
     pass

As it is, this view won’t do anything, as it has no get, post or other methods. What it does provide is Django’s MultipleObjectMixin, along with nap’s MapperMixin and NapView classes.

To add the default GET behavior for a list, we mix in the ListGetMixin:

polls/views.py
 class QuestionListView(QuestionMixin,
                        views.ListGetMixin,
                        views.BaseListView):
     pass

The ListGetMixin adds a simple get method, which will return a list of mapped instances of our model.

Let’s add our new view to the existing urls, but with a ‘api/’ prefix:

polls/urls.py
from django.conf.urls import url

from . import views

urlpatterns = [
    # ex: /polls/
    url(r'^$', views.index, name='index'),
    # ex: /polls/5/
    url(r'^(?P<question_id>[0-9]+)/$', views.detail, name='detail'),
    # ex: /polls/5/results/
    url(r'^(?P<question_id>[0-9]+)/results/$', views.results, name='results'),
    # ex: /polls/5/vote/
    url(r'^(?P<question_id>[0-9]+)/vote/$', views.vote, name='vote'),

    url(r'^api/', include([
      url(r'question/$', views.QuestionListView.as_view()),
    ]))
]

So we can now access our list of Questions at http://localhot:8000/api/question/ and should see something like this:

[
   {
      "id": 1,
      "question_text": "What's new?",
      "pub_date": "2017-06-17 05:30:58+00:00",
      "age": "20\u00a0hours, 15\u00a0minutes"
   }
]

Nested Records

That’s great, but a Question with no Choices isn’t much use, is it?

We can ask our mapper to render a list of related records using a ToMany field:

polls/mappers.py
class QuestionMapper(mapper.ModelMapper):
   class Meta:
        model = models.Question
        fields = '__all__'

   @mapper.field
   def age(self):
        return timesince(self.pub_date)

   choices = mapper.ToManyField('choice_set')

The ToManyField will check if its value is a django.db.models.Manager, and call .all() on it if it is.

And now out output will look something like this:

[
   {
      "id": 1,
      "age": "20\u00a0hours, 19\u00a0minutes",
      "question_text": "What's new?",
      "pub_date": "2017-06-17 05:30:58+00:00",
      "choices": [1, 2]
   }
]

By default, a ToManyField will only render the primary keys of the related objects. If you want to control how it’s serialised, just specify a mapper on the field.

polls/mappers.py
choices = mapper.ToManyField('choice_set', mapper=ChoiceMapper)

Which will give us this output:

[
   {
      "pub_date": "2017-06-17 05:30:58+00:00",
      "age": "20\u00a0hours, 22\u00a0minutes",
      "question_text": "What's new?",
      "id": 1,
      "choices": [
         {
            "question": 1,
            "choice_text": "First Choice",
            "id": 1,
            "votes": 0
         },
         {
            "question": 1,
            "choice_text": "Another Choice",
            "id": 2,
            "votes": 0
         }
      ]
   }
]

We really don’t need the question ID embedded there, so let’s define a new choice mapper which will exclude that.

polls/mappers.py
 class InlineChoiceMapper(mapper.ModelMapper):
     class Meta:
         model = models.Choice
         fields = '__all__'
         exclude = ('question',)

And finally we see:

[
   {
      "choices": [
         {
            "votes": 0,
            "id": 1,
            "choice_text": "First Choice"
         },
         {
            "votes": 0,
            "id": 2,
            "choice_text": "Another Choice"
         }
      ],
      "question_text": "What's new?",
      "age": "20\u00a0hours, 27\u00a0minutes",
      "pub_date": "2017-06-17 05:30:58+00:00",
      "id": 1
   }
]