1. # Creating a production ready API with Python and Django Rest Framework – part 4

In the previous part of the tutorial we implemented details management, relations between models, nested APIs and a different level of permissions. Our API is basically complete but it is working properly? Is the source code free of bugs? Would you feel confident to refactor the code without breaking something? The answer to all our question is probably no. I can't be sure if the code behaves properly nor I would feel confident refactoring anything without having some tests coverage.

As I mentioned previously, we should have written tests since the beginning, but I really didn't want to mix too many concepts together and I wanted to let the user concentrate on the Rest Framework instead.

### Test structure and configuration

Before beginning the fourth part of this tutorial, make sure you have grabbed the latest source code from https://github.com/andreagrandi/drf-tutorial and you have checked out the previous git tag:

git checkout tutorial-1.14


Django has an integrated test runner but my personal choice is to use pytest, so as first thing let's install the needed libraries:

pip install pytest pytest-django


As long as we respect a minimum of conventions (test files must start with test_ prefix), tests can be placed anywhere in the code. My advice is to put them all together in a separate folder and divide them according to app names. In our case we are going to create a folder named "tests" at the same level of manage.py file. Inside this folder we need to create a __init__.py file and another folder called catalog with an additional __init__.py inside. Now, still at the same level of manage.py create a file called pytest.ini with this content:

[pytest]
DJANGO_SETTINGS_MODULE=drftutorial.settings


Are you feeling confused? No problem. You can checkout the source code containing these changes.

git checkout tutorial-1.15


You can check if you have done everything correctly going inside the drftutorial folder (the one containing manage.py) and launching pytest. If you see something like this, you did your changes correctly:

(drf-tutorial) ➜  drftutorial git:(master) pytest
============================================================================================================================= test session starts ==============================================================================================================================
platform darwin -- Python 2.7.13, pytest-3.0.6, py-1.4.32, pluggy-0.4.0
Django settings: drftutorial.settings (from ini file)
rootdir: /Users/andrea/Projects/drf-tutorial/drftutorial, inifile: pytest.ini
plugins: django-3.1.2
collected 0 items

========================================================================================================================= no tests ran in 0.01 seconds =========================================================================================================================
(drf-tutorial) ➜  drftutorial git:(master)


### Writing the first test

To begin with, I will show you how to write a simple test that will verify if the API can return the products list. If you remember we implemented this API in the first part of the tutorial. First of all create a file called test_views.py under the folder drftutorial/tests/catalog/ and add this code:

import pytest
from django.urls import reverse
from rest_framework import status
from rest_framework.test import APITestCase

class TestProductList(APITestCase):
@pytest.mark.django_db
def test_can_get_product_list(self):
url = reverse('product-list')
response = self.client.get(url)
self.assertEqual(response.status_code, status.HTTP_200_OK)
self.assertEqual(len(response.json()), 8)


before being able to run this test we need to change a little thing in the catalog/urls.py file, something we should have done since the beginning. Please change the first url in this way, adding the name parameter:

urlpatterns = [
url(r'^products/(?P<pk>[0-9]+)/$', views.ProductDetail.as_view()), ]  If we try to PUT, DELETE or GET a product like /products/1/ we can now update, delete or retrieve an existing item, but there is a little problem: we haven't set any permission on this class, so anyone can do it. The previous view was also more compact, why don't we use a generic view to perform these basic operations? Let's refactor ProductDetail with a RetrieveUpdateDestroyAPIView generic class. Open catalog/views.py and change the class code in this way: class ProductDetail(generics.RetrieveUpdateDestroyAPIView): queryset = Product.objects.all() serializer_class = ProductSerializer permission_classes = (IsAdminOrReadOnly, )  That's it! With just three lines of code we have now implemented the same feature of the previous class, plus we have set the correct permissions. To checkout the code at this point: git checkout tutorial-1.12  ### Reviews - Relations between models As many online catalogs already have, it would be nice if our API had an endpoint where it is possible to leave a review for a product and get a list of reviews for a specific product. To implement this feature we need to add a new model to our application. Edit catalog/models.py adding this import: from django.contrib.auth.models import User  and this Django model: class Review(models.Model): product = models.ForeignKey(Product, related_name='reviews') title = models.CharField(max_length=255) review = models.TextField() rating = models.IntegerField() created_by = models.ForeignKey(User)  after creating the model, please remember to create the related DB migration: $ ./manage.py makemigrations catalog


When the model is ready, we have to do some changes to the serializers. First of all we need to write a new one, for our new Review model. Then we have to change our ProductSerializer so that it will return its related reviews. Each Product can have multiple Review. And each Review will be always linked to a specific Product. Edit catalog/serializers.py and change it in this way:

from .models import Product, Review
from rest_framework import serializers

class ReviewSerializer(serializers.ModelSerializer):

class Meta:
model = Review
fields = ('id', 'title', 'review', 'rating', 'created_by')

class ProductSerializer(serializers.ModelSerializer):

class Meta:
model = Product
fields = ('id', 'name', 'description', 'price', 'reviews')


Note: in ReviewSerializer when we serialise the user contained in created_by field, return the username instead of the id (to make it more human readable). Another important thing to notice is that the value of the related_name we have set in the Review model must match with the field name we have added in ProductSerializer fields property. In this case we have set it to reviews.

At this point we need to add a new view. Edit catalog/views.py and add the following imports:

from rest_framework.permissions import IsAuthenticatedOrReadOnly
from .models import Product, Review
from .serializers import ProductSerializer, ReviewSerializer


class ReviewList(generics.ListCreateAPIView):
queryset = Review.objects.all()
serializer_class = ReviewSerializer

def perform_create(self, serializer):
serializer.save(
created_by=self.request.user,
product_id=self.kwargs['pk'])


As you can notice, I had to customise the perform_create method because the default one doesn't know anything about the fact we want to set the created_by and product_id fields. Finally we need to bind this new view to a specific url, so we need to edit catalog/urls.py and add this:

...
url(r'^products/(?P<pk>[0-9]+)/reviews/$', views.ReviewList.as_view()), ]  At this point any authenticated user should be able to POST a review for a product and anyone should be able to get the list of reviews for each product. If you have any problem with the code and want to move to this point, please checkout this: git checkout tutorial-1.13  ### Nested APIs details To complete our API endpoints for Review, we need to add an additional feature that will let users to edit/delete their own review. Before implementing the new view, we need a little bit of refactoring and a new permission class. Edit catalog/permissions.py and add this new class: class IsOwnerOrReadOnly(BasePermission): def has_object_permission(self, request, view, obj): if request.method in SAFE_METHODS: return True return obj.created_by == request.user  Basically this will permit changes to the review only to its author. Now we are going to add new urls and doing some refactoring at the same time. Edit catalog/urls.py and change the urls in this way: urlpatterns = [ url(r'^products/$', views.ProductList.as_view()),
url(r'^products/(?P<product_id>[0-9]+)/$', views.ProductDetail.as_view()), url( r'^products/(?P<product_id>[0-9]+)/reviews/$',
views.ReviewList.as_view()
),
url(
r'^products/(?P<product_id>[0-9]+)/reviews/(?P<review_id>[0-9]+)/\$',
views.ReviewDetail.as_view()
),
]


You may have noticed that I substituted pk with product_id. In the latest url I added, we need to be able to identify two primary keys: the one for the product and the one for the review. I renamed the previous ones for consistency. Now it's time to add the new view for Review details. Edit catalog/view.py and add this class:

class ReviewDetail(generics.RetrieveUpdateDestroyAPIView):
serializer_class = ReviewSerializer
lookup_url_kwarg = 'review_id'

def get_queryset(self):
review = self.kwargs['review_id']
return Review.objects.filter(id=review)


What are we doing here? You may have noticed that we set a new property called lookup_url_kwarg. That property is being used to determine the keyword in urls.py to be used for the primary key lookup.

You will also need to do some refactoring to the other views, to adapt them to the changes we just did to the urls. I suggest you to have a look at the diffs here: https://github.com/andreagrandi/drf-tutorial/compare/tutorial-1.13...tutorial-1.14 or you can have a look at the whole file here https://github.com/andreagrandi/drf-tutorial/blob/541bf31c11fd1dbf2bcc1d31312086995e3e5b48/drftutorial/catalog/views.py

In alternative, you can fetch the whole source code at this point:

git checkout tutorial-1.14


### Wrapping Up

In this third part of the tutorial you learned how to handle model details in the API and how relations between different model work. In the next part of the tutorial we will do something we should have done since the beginning: adding tests to our code and learn how to properly test the API.