# Tutorial 3: Class-based Views

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 [DRY][dry].

## Rewriting our API using class-based views

We'll start by rewriting the root view as a class-based view.  All this involves is a little bit of refactoring of `views.py`.

```python
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)
```

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 `views.py`.

```python
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)
```

That's looking good.  Again, it's still pretty similar to the function based view right now.

We'll also need to refactor our `snippets/urls.py` slightly now that we're using class-based views.

```python
from django.urls import path
from rest_framework.urlpatterns import format_suffix_patterns
from snippets import views

urlpatterns = [
    path("snippets/", views.SnippetList.as_view()),
    path("snippets/<int:pk>/", views.SnippetDetail.as_view()),
]

urlpatterns = format_suffix_patterns(urlpatterns)
```

Okay, we're done.  If you run the development server everything should be working just as before.

## Using mixins

One of the big wins of using class-based views is that it allows us to easily compose reusable bits of behavior.

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 behavior are implemented in REST framework's mixin classes.

Let's take a look at how we can compose the views by using the mixin classes.  Here's our `views.py` module again.

```python
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)
```

We'll take a moment to examine exactly what's happening here.  We're building our view using `GenericAPIView`, and adding in `ListModelMixin` and `CreateModelMixin`.

The base class provides the core functionality, and the mixin classes provide the `.list()` and `.create()` actions.  We're then explicitly binding the `get` and `post` methods to the appropriate actions.  Simple enough stuff so far.

```python
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)
```

Pretty similar.  Again we're using the `GenericAPIView` class to provide the core functionality, and adding in mixins to provide the `.retrieve()`, `.update()` and `.destroy()` actions.

## Using generic class-based views

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 `views.py` module even more.

```python
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
```

Wow, that's pretty concise.  We've gotten a huge amount for free, and our code looks like good, clean, idiomatic Django.

Next we'll move onto [part 4 of the tutorial][tut-4], where we'll take a look at how we can deal with authentication and permissions for our API.

[dry]: https://en.wikipedia.org/wiki/Don't_repeat_yourself
[tut-4]: 4-authentication-and-permissions.md
