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  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/$', views.ProductList.as_view(), name='product-list'),
        ...
    

    at this point we are able to run our test suite again and verify the test is passing:

    (drf-tutorial) ➜  drftutorial git:(test-productlist) ✗ pytest -v
    ============================================================================================================================= test session starts ==============================================================================================================================
    platform darwin -- Python 2.7.13, pytest-3.0.6, py-1.4.32, pluggy-0.4.0 -- /Users/andrea/.virtualenvs/drf-tutorial/bin/python2.7
    cachedir: .cache
    Django settings: drftutorial.settings (from ini file)
    rootdir: /Users/andrea/Projects/drf-tutorial/drftutorial, inifile: pytest.ini
    plugins: django-3.1.2
    collected 1 items
    
    tests/catalog/test_views.py::TestProductList::test_can_get_product_list PASSED
    
    =========================================================================================================================== 1 passed in 0.98 seconds ===========================================================================================================================
    

    To checkout the source code at this point:

    git checkout tutorial-1.16
    

    Explaining the test code

    When we implement a test, the first thing to do is to create a test_* file and import the minimum necessary to write a test class and method. Each test class must inherit from APITestCase and have a name that start with Test, like TestProductList. Since we use pytest, we need to mark our method with @pytest.mark.django_db decorator, to tell the test suite our code will explicitly access the database. We are going to use the client object that is integrated in APITestCase to perform the request. Before doing that we first get the local url using Django's reverse function. At this point we do the call using the client:

    response = self.client.get(url)
    

    and then we assert a couple of things that we expect to be true:

    self.assertEqual(response.status_code, status.HTTP_200_OK)
    self.assertEqual(len(response.json()), 8)
    

    We check that our API returns the 200 status code and that in the returned JSON there are 8 elements.

    It's normally a good practice to create test data inside the tests, but in our case we previously created a data migration that creates test data. Migrations are run every time we run tests so when we call our API, the data will be already there.

    Wrapping up

    I've written a few tests for all the views we have implemented until now and they are available if you checkout this version of the code:

    git checkout tutorial-1.17
    

    I've only tested the views but it would be nice to test even the permission class, for example. Please remember to write your tests first, if possible: implementing the code will be much more natural once the tests are already in place.

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  2. Migrating from WordPress to a static generated website

    As you may have noticed, my website looks very different compared to a few days ago. It's just a different theme or template, I completely changed how the pages are generated and I'm hosting it in a completely different way.

    A brief history

    When I started this blog 10 years ago, I was hosting it on a shared hosting service and it was based on WordPress. I then decided to keep WordPress as backend (I don't like PHP very much but I wasn't even good at front end development at the time, so using a tool that allowed me to concentrate on the content rather than on design was a natural choice for me) but to move my website to a VPS on DigitalOcean, where I've self-hosted Nginx + PHP + MySQL and even Postfix for email aliases until a few days ago.

    Why moving to a static website?

    In these three or four years I've been using a VPS, I must say I've been good enough (or maybe lucky?) at keeping "bad people" out of my server, but it's true that maintaining a VPS can be very time consuming and you can never be sure that your website is always safe. I've heard about static website before, but I was a bit skeptic because I had not spent enough time investigating all the possibilities (search and comments are still possible, thanks to external services and plugins).

    Another advantage of a static website is that I can perfectly "run" (preview) on my local computer without publishing it online. Pages can be rendered locally and will appear in the browser exactly as they will appear once published online.

    If you use a tool like WordPress, you need to be constantly connected to Internet to write any change. With static pages I can write my content offline (so I can do it while commuting on the train or while I'm flying somewhere) and publish it once I'm back online.

    Pelican

    The tool that I'm using to generate this website is called Pelican. There are many static website generators, the reason why I chose Pelican is because it's written in Python, so if I need to do any change I can do them and because its templates use Jinja2 which I'm already familiar with. It can also import posts from WordPress (and I had over 180 posts to import from my previous website) so if you are migrating from it it's a good choice. Please note that the import script is not perfect and that you may have to adjust some formatting here and there.

    A new deployment pipeline

    When you use WordPress your website is already online and all you have to do is to login, use the integrated editor, write content and finally publish it. A static website doesn't have any admin tool, it's just static pages. How do you publish content then? There are of course multiple solutions available. In my case my website source code is hosted in a repository on GitHub. When I commit on master branch there is a webhook that triggers a build job on TravisCI. TravisCI fetches the latest source code, installs Pelican on the CI and builds the static pages. Once the build is finished, a bash script is used to publish the generated pages on the static website hosting service.

    Hosting a static website

    The good thing about hosting a static website is that you don't need a database so you can host it almost anywhere at a cheaper price or even for free. In my case I've decided to use GitHub pages, mainly for simplicity. Every GitHub user can have a static website hosted at <yourusername>.github.io for free. To start using it, you just have to create a repository named <yourusername>.github.io under your GitHub account. In my case the repository is https://github.com/andreagrandi/andreagrandi.github.io. My deploy script simply takes the generated content that is in the output/ folder and git push it on this repository. Once the website has been pushed to git, it's immediately available at https://andreagrandi.github.io

    CloudFlare

    GitHub Pages service has a little limitation: you can either have your website served from a URL similar to the one I've just mentioned, including SSL support or you can use your own domain, but you can't have both things (SSL + custom domain). To workaround this, you can instruct your domain registrar (in my case is Gandi.net) to let CloudFlare manage your domain and just enabling "Full SSL" support will do the trick. I won't repeat here how to use CloudFlare since they have a very nice tutorial explaining how to configure their service to be used with GitHub Pages: https://blog.cloudflare.com/secure-and-fast-github-pages-with-cloudflare/. Remember to include a CNAME file containing your domain name and let your static generetor put it on the root of your website, otherwise GitHub pages won't serve the pages correctly.

    Why not Amazon S3?

    While I was looking for instructions about how to host a static websites, I found many examples of websites using Amazon S3. There is nothing wrong with using this service (just keep in mind that it's not free, Amazon charges you for space usage and requests, so keep an eye on the AWS bill) but the way these websites were using it was completely wrong. The most common error I noticed was the fact they were enabling the flexible SSL option on CloudFlare: this means that the connection between the visitor and CloudFlare was encrypted (and visitor could see the the SSL enabled) but the connection between CloudFlare and Amazon S3 was being served with HTTP only, meaning that potentially the pages could have been modified before being served. Infact Amazon doesn't serve the S3 website buckets with SSL, they use plain HTTP (Why are you doing this Amazon?!). To use the S3 bucket correctly one should also configure Route 53 (to manage DNS) and CloudFront (the Amazon equivalent of CloudFlare service, beware because this is also charged separately depending on usage/traffic), making the whole setup a bit more complicated.

    Conclusion

    I finally moved away from my VPS and from now on I will be able to concentrate my time on content only instead of spending part of it to maintain my server. Last but not least, the possibility to write my content offline, will hopefully allow me to write from places (train, airplane) where I've never written from before. If you have any suggestion or if if you notice any error, feel free to leave a comment here below. In alternative, since now this blog is completely open source and on GitHub, you can fork it and make a pull request!

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  3. Creating a production ready API with Python and Django Rest Framework – part 3

    In the previous part we implemented authentication, permissions and the possibility to POST new products for admins. In this new episode we will see how to implement details management, relations between models, nested APIs and a different level of permissions.

    If you haven't completed the previous parts or if you want to begin from this one, checkout the right code first:

    git checkout tutorial-1.10
    

    Handling Product Details

    Our current API methods allow us to list all the products we have in our catalog and to create a new one (if we have admin permissions), but what if we wanted to delete or update a single one? What if we wanted to get only a specific product? We need to handle details.

    As first thing we need to change the ProductSerializer to return the id of the product. Edit catalog/serializers.py and change the class in this way:

    class ProductSerializer(serializers.ModelSerializer):
        class Meta:
            model = Product
            fields = ('id', 'name', 'description', 'price')
    

    After changing the serializer we need to implement a new view called ProductDetail. Edit catalog/views.py and add the following imports:

    from django.http import Http404
    from rest_framework.response import Response
    from rest_framework.views import APIView
    from rest_framework import status
    

    and the following class:

    class ProductDetail(APIView):
        def get_object(self, pk):
            try:
                return Product.objects.get(pk=pk)
            except Product.DoesNotExist:
                raise Http404
    
        def get(self, request, pk, format=None):
            product = self.get_object(pk)
            serializer = ProductSerializer(product)
            return Response(serializer.data)
    
        def put(self, request, pk, format=None):
            product = self.get_object(pk)
            serializer = ProductSerializer(product, data=request.data)
            if serializer.is_valid():
                serializer.save()
                return Response(serializer.data)
            return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
    
        def delete(self, request, pk, format=None):
            product = self.get_object(pk)
            product.delete()
            return Response(status=status.HTTP_204_NO_CONTENT)
    

    let's connect the new view to the urls, editing catalog/urls.py and changing the code in this way:

    urlpatterns = [
        url(r'^products/$', views.ProductList.as_view()),
        url(r'^products/(?P<pk>[0-9]+)/$', 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):
        created_by = serializers.ReadOnlyField(source='created_by.username')
    
        class Meta:
            model = Review
            fields = ('id', 'title', 'review', 'rating', 'created_by')
    
    
    class ProductSerializer(serializers.ModelSerializer):
        reviews = ReviewSerializer(many=True, read_only=True)
    
        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
    

    then add this class:

    class ReviewList(generics.ListCreateAPIView):
        queryset = Review.objects.all()
        serializer_class = ReviewSerializer
        permission_classes = (IsAuthenticatedOrReadOnly, )
    
        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
        permission_classes = (IsAuthenticatedOrReadOnly, IsOwnerOrReadOnly)
        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.

    Feedback Please

    If you enjoyed this tutorial, please leave me some feedback! I really want to improve my work, based on the users feedback so any little advice will be appreciated, thanks!

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