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                    <a href="#tutorial-3-class-based-views">Tutorial 3: Class Based Views</a>
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                    <li>
                      <a href="#rewriting-our-api-using-class-based-views">Rewriting our API using class based views</a>
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                      <a href="#using-mixins">Using mixins</a>
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            <h1 id="tutorial-3-class-based-views">Tutorial 3: Class Based Views</h1>
<p>We can also write our API views using class based views, rather than function based views.  As we'll see this is a powerful pattern that allows us to reuse common functionality, and helps us keep our code <a href="http://en.wikipedia.org/wiki/Don't_repeat_yourself">DRY</a>.</p>
<h2 id="rewriting-our-api-using-class-based-views">Rewriting our API using class based views</h2>
<p>We'll start by rewriting the root view as a class based view.  All this involves is a little bit of refactoring of <code>views.py</code>.</p>
<pre><code>from snippets.models import Snippet
from snippets.serializers import SnippetSerializer
from django.http import Http404
from rest_framework.views import APIView
from rest_framework.response import Response
from rest_framework import status


class SnippetList(APIView):
    """
    List all snippets, or create a new snippet.
    """
    def get(self, request, format=None):
        snippets = Snippet.objects.all()
        serializer = SnippetSerializer(snippets, many=True)
        return Response(serializer.data)

    def post(self, request, format=None):
        serializer = SnippetSerializer(data=request.data)
        if serializer.is_valid():
            serializer.save()
            return Response(serializer.data, status=status.HTTP_201_CREATED)
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
</code></pre>
<p>So far, so good.  It looks pretty similar to the previous case, but we've got better separation between the different HTTP methods.  We'll also need to update the instance view in <code>views.py</code>.</p>
<pre><code>class SnippetDetail(APIView):
    """
    Retrieve, update or delete a snippet instance.
    """
    def get_object(self, pk):
        try:
            return Snippet.objects.get(pk=pk)
        except Snippet.DoesNotExist:
            raise Http404

    def get(self, request, pk, format=None):
        snippet = self.get_object(pk)
        serializer = SnippetSerializer(snippet)
        return Response(serializer.data)

    def put(self, request, pk, format=None):
        snippet = self.get_object(pk)
        serializer = SnippetSerializer(snippet, 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):
        snippet = self.get_object(pk)
        snippet.delete()
        return Response(status=status.HTTP_204_NO_CONTENT)
</code></pre>
<p>That's looking good.  Again, it's still pretty similar to the function based view right now.</p>
<p>We'll also need to refactor our <code>urls.py</code> slightly now we're using class based views.</p>
<pre><code>from django.conf.urls import url
from rest_framework.urlpatterns import format_suffix_patterns
from snippets import views

urlpatterns = [
    url(r'^snippets/$', views.SnippetList.as_view()),
    url(r'^snippets/(?P&lt;pk&gt;[0-9]+)/$', views.SnippetDetail.as_view()),
]

urlpatterns = format_suffix_patterns(urlpatterns)
</code></pre>
<p>Okay, we're done.  If you run the development server everything should be working just as before.</p>
<h2 id="using-mixins">Using mixins</h2>
<p>One of the big wins of using class based views is that it allows us to easily compose reusable bits of behaviour.</p>
<p>The create/retrieve/update/delete operations that we've been using so far are going to be pretty similar for any model-backed API views we create.  Those bits of common behaviour are implemented in REST framework's mixin classes.</p>
<p>Let's take a look at how we can compose the views by using the mixin classes.  Here's our <code>views.py</code> module again.</p>
<pre><code>from snippets.models import Snippet
from snippets.serializers import SnippetSerializer
from rest_framework import mixins
from rest_framework import generics

class SnippetList(mixins.ListModelMixin,
                  mixins.CreateModelMixin,
                  generics.GenericAPIView):
    queryset = Snippet.objects.all()
    serializer_class = SnippetSerializer

    def get(self, request, *args, **kwargs):
        return self.list(request, *args, **kwargs)

    def post(self, request, *args, **kwargs):
        return self.create(request, *args, **kwargs)
</code></pre>
<p>We'll take a moment to examine exactly what's happening here.  We're building our view using <code>GenericAPIView</code>, and adding in <code>ListModelMixin</code> and <code>CreateModelMixin</code>.</p>
<p>The base class provides the core functionality, and the mixin classes provide the <code>.list()</code> and <code>.create()</code> actions.  We're then explicitly binding the <code>get</code> and <code>post</code> methods to the appropriate actions.  Simple enough stuff so far.</p>
<pre><code>class SnippetDetail(mixins.RetrieveModelMixin,
                    mixins.UpdateModelMixin,
                    mixins.DestroyModelMixin,
                    generics.GenericAPIView):
    queryset = Snippet.objects.all()
    serializer_class = SnippetSerializer

    def get(self, request, *args, **kwargs):
        return self.retrieve(request, *args, **kwargs)

    def put(self, request, *args, **kwargs):
        return self.update(request, *args, **kwargs)

    def delete(self, request, *args, **kwargs):
        return self.destroy(request, *args, **kwargs)
</code></pre>
<p>Pretty similar.  Again we're using the <code>GenericAPIView</code> class to provide the core functionality, and adding in mixins to provide the <code>.retrieve()</code>, <code>.update()</code> and <code>.destroy()</code> actions.</p>
<h2 id="using-generic-class-based-views">Using generic class based views</h2>
<p>Using the mixin classes we've rewritten the views to use slightly less code than before, but we can go one step further.  REST framework provides a set of already mixed-in generic views that we can use to trim down our <code>views.py</code> module even more.</p>
<pre><code>from snippets.models import Snippet
from snippets.serializers import SnippetSerializer
from rest_framework import generics


class SnippetList(generics.ListCreateAPIView):
    queryset = Snippet.objects.all()
    serializer_class = SnippetSerializer


class SnippetDetail(generics.RetrieveUpdateDestroyAPIView):
    queryset = Snippet.objects.all()
    serializer_class = SnippetSerializer
</code></pre>
<p>Wow, that's pretty concise.  We've gotten a huge amount for free, and our code looks like good, clean, idiomatic Django.</p>
<p>Next we'll move onto <a href="../4-authentication-and-permissions">part 4 of the tutorial</a>, where we'll take a look at how we can deal with authentication and permissions for our API.</p>

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