Class-based views

Class-based views

A view is a callable which takes a request and returns a response. This can be more than just a function, and Django provides an example of some classes which can be used as views. These allow you to structure your views and reuse code by harnessing inheritance and mixins. There are also some generic views for tasks which we’ll get to later, but you may want to design your own structure of reusable views which suits your use case. For full details, see the class-based views reference documentation.

Basic examples

Django provides base view classes which will suit a wide range of applications. All views inherit from the View class, which handles linking the view into the URLs, HTTP method dispatching and other common features. RedirectView provides a HTTP redirect, and TemplateView extends the base class to make it also render a template.

Usage in your URLconf

The most direct way to use generic views is to create them directly in your URLconf. If you’re only changing a few attributes on a class-based view, you can pass them into the as_view() method call itself:

from django.urls import path
from django.views.generic import TemplateView
urlpatterns = [
    path("about/", TemplateView.as_view(template_name="about.html")),
]

Any arguments passed to as_view() will override attributes set on the class. In this example, we set template_name on the TemplateView. A similar overriding pattern can be used for the url attribute on RedirectView.

Subclassing generic views

The second, more powerful way to use generic views is to inherit from an existing view and override attributes (such as the template_name) or methods (such as get_context_data) in your subclass to provide new values or methods. Consider, for example, a view that just displays one template, about.html. Django has a generic view to do this - TemplateView - so we can subclass it, and override the template name:

# some_app/views.py
from django.views.generic import TemplateView
class AboutView(TemplateView):
    template_name = "about.html"

Then we need to add this new view into our URLconf. TemplateView is a class, not a function, so we point the URL to the as_view() class method instead, which provides a function-like entry to class-based views:

# urls.py
from django.urls import path
from some_app.views import AboutView
urlpatterns = [
    path("about/", AboutView.as_view()),
]

For more information on how to use the built in generic views, consult the next topic on generic class-based views.

Supporting other HTTP methods

Suppose somebody wants to access our book library over HTTP using the views as an API. The API client would connect every now and then and download book data for the books published since last visit. But if no new books appeared since then, it is a waste of CPU time and bandwidth to fetch the books from the database, render a full response and send it to the client. It might be preferable to ask the API when the most recent book was published.

We map the URL to book list view in the URLconf:

from django.urls import path
from books.views import BookListView
urlpatterns = [
    path("books/", BookListView.as_view()),
]

And the view:

from django.http import HttpResponse
from django.views.generic import ListView
from books.models import Book
class BookListView(ListView):
    model = Book
    def head(self, *args, **kwargs):
        last_book = self.get_queryset().latest("publication_date")
        response = HttpResponse(
            # RFC 1123 date format.
            headers={
                "Last-Modified": last_book.publication_date.strftime(
                    "%a, %d %b %Y %H:%M:%S GMT"
                )
            },
        )
        return response

If the view is accessed from a GET request, an object list is returned in the response (using the book_list.html template). But if the client issues a HEAD request, the response has an empty body and the Last-Modified header indicates when the most recent book was published. Based on this information, the client may or may not download the full object list.

Asynchronous class-based views

New in Django 4.1.

As well as the synchronous (def) method handlers already shown, View subclasses may define asynchronous (async def) method handlers to leverage asynchronous code using await:

import asyncio
from django.http import HttpResponse
from django.views import View
class AsyncView(View):
    async def get(self, request, *args, **kwargs):
        # Perform io-blocking view logic using await, sleep for example.
        await asyncio.sleep(1)
        return HttpResponse("Hello async world!")

Within a single view-class, all user-defined method handlers must be either synchronous, using def, or all asynchronous, using async def. An ImproperlyConfigured exception will be raised in as_view() if def and async def declarations are mixed.

Django will automatically detect asynchronous views and run them in an asynchronous context. You can read more about Django’s asynchronous support, and how to best use async views, in Asynchronous support.