Django 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 simple 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.

Introduction to Class-based views

Class-based generic views

Form handling with class-based views

Using mixins with class-based views

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 in to the URLs, HTTP method dispatching and other simple features. RedirectView is
for a simple HTTP redirect, and TemplateView extends
the base class to make it also render a template.

Simple usage in your URLconf

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

from django.conf.urls import patterns
from django.views.generic import TemplateView

urlpatterns = patterns('',
(r'^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 theTemplateView.
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 thetemplate_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 just 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 just need to add this new view into our URLconf. TemplateView is
a class, not a function, so we point the URL to theas_view() class
method instead, which provides a function-like entry to class-based views:

# urls.py
from django.conf.urls import patterns
from some_app.views import AboutView

urlpatterns = patterns('',
(r'^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.conf.urls import patterns
from books.views import BookListView

urlpatterns = patterns('',
(r'^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
response['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, a plain-and-simple object list is returned in the
response (using book_list.htmltemplate). 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.