Note
Prior to Django 1.3, generic views were implemented as functions. The function-based implementation has been deprecated in favor of the class-based approach described here.
For details on the previous generic views implementation, see the topic guide and detailed reference.
Writing Web applications can be monotonous, because we repeat certain patterns again and again. Django tries to take away some of that monotony at the model and template layers, but Web developers also experience this boredom at the view level.
Django’s generic views were developed to ease that pain. They take certain common idioms and patterns found in view development and abstract them so that you can quickly write common views of data without having to write too much code.
We can recognize certain common tasks, like displaying a list of objects, and write code that displays a list of any object. Then the model in question can be passed as an extra argument to the URLconf.
Django ships with generic views to do the following:
TalkListView and a
RegisteredUserListView would be examples of list views. A single
talk page is an example of what we call a “detail” view.Taken together, these views provide easy interfaces to perform the most common tasks developers encounter.
Class-based generic views (and any class-based views that inherit from the base classes Django provides) can be configured in two ways: subclassing, or passing in arguments directly in the URLconf.
When you subclass a class-based view, you can 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 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. As the class-based
views themselves are classes, we point the URL to the as_view class method
instead, which is the entry point for class-based views:
# urls.py
from django.conf.urls import patterns, url, include
from some_app.views import AboutView
urlpatterns = patterns('',
(r'^about/', AboutView.as_view()),
)
Alternatively, if you’re only changing a few simple attributes on a
class-based view, you can simply pass the new attributes into the as_view
method call itself:
from django.conf.urls import patterns, url, include
from django.views.generic import TemplateView
urlpatterns = patterns('',
(r'^about/', TemplateView.as_view(template_name="about.html")),
)
A similar overriding pattern can be used for the url attribute on
RedirectView, another simple
generic view.
TemplateView certainly is useful,
but Django’s generic views really shine when it comes to presenting
views of your database content. Because it’s such a common task,
Django comes with a handful of built-in generic views that make
generating list and detail views of objects incredibly easy.
Let’s take a look at one of these generic views: the “object list” view. We’ll be using these models:
# models.py
from django.db import models
class Publisher(models.Model):
name = models.CharField(max_length=30)
address = models.CharField(max_length=50)
city = models.CharField(max_length=60)
state_province = models.CharField(max_length=30)
country = models.CharField(max_length=50)
website = models.URLField()
class Meta:
ordering = ["-name"]
def __unicode__(self):
return self.name
class Book(models.Model):
title = models.CharField(max_length=100)
authors = models.ManyToManyField('Author')
publisher = models.ForeignKey(Publisher)
publication_date = models.DateField()
To build a list page of all publishers, we’d use a URLconf along these lines:
from django.conf.urls import patterns, url, include
from django.views.generic import ListView
from books.models import Publisher
urlpatterns = patterns('',
(r'^publishers/$', ListView.as_view(
model=Publisher,
)),
)
That’s all the Python code we need to write. We still need to write a template,
however. We could explicitly tell the view which template to use
by including a template_name key in the arguments to as_view, but in
the absence of an explicit template Django will infer one from the object’s
name. In this case, the inferred template will be
"books/publisher_list.html" – the “books” part comes from the name of the
app that defines the model, while the “publisher” bit is just the lowercased
version of the model’s name.
Note
Thus, when (for example) the django.template.loaders.app_directories.Loader
template loader is enabled in TEMPLATE_LOADERS, the template
location would be:
/path/to/project/books/templates/books/publisher_list.html
This template will be rendered against a context containing a variable called
object_list that contains all the publisher objects. A very simple template
might look like the following:
{% extends "base.html" %}
{% block content %}
<h2>Publishers</h2>
<ul>
{% for publisher in object_list %}
<li>{{ publisher.name }}</li>
{% endfor %}
</ul>
{% endblock %}
That’s really all there is to it. All the cool features of generic views come from changing the “info” dictionary passed to the generic view. The generic views reference documents all the generic views and their options in detail; the rest of this document will consider some of the common ways you might customize and extend generic views.
There’s no question that using generic views can speed up development substantially. In most projects, however, there comes a moment when the generic views no longer suffice. Indeed, the most common question asked by new Django developers is how to make generic views handle a wider array of situations.
This is one of the reasons generic views were redesigned for the 1.3 release - previously, they were just view functions with a bewildering array of options; now, rather than passing in a large amount of configuration in the URLconf, the recommended way to extend generic views is to subclass them, and override their attributes or methods.
You might have noticed that our sample publisher list template stores
all the publishers in a variable named object_list. While this
works just fine, it isn’t all that “friendly” to template authors:
they have to “just know” that they’re dealing with publishers here.
Well, if you’re dealing with a model object, this is already done for
you. When you are dealing with an object or queryset, Django is able
to populate the context using the verbose name (or the plural verbose
name, in the case of a list of objects) of the object being displayed.
This is provided in addition to the default object_list entry, but
contains exactly the same data.
If the verbose name (or plural verbose name) still isn’t a good match,
you can manually set the name of the context variable. The
context_object_name attribute on a generic view specifies the
context variable to use. In this example, we’ll override it in the
URLconf, since it’s a simple change:
urlpatterns = patterns('',
(r'^publishers/$', ListView.as_view(
model=Publisher,
context_object_name="publisher_list",
)),
)
Providing a useful context_object_name is always a good idea. Your
coworkers who design templates will thank you.
Often you simply need to present some extra information beyond that
provided by the generic view. For example, think of showing a list of
all the books on each publisher detail page. The
DetailView generic view provides
the publisher to the context, but it seems there’s no way to get
additional information in that template.
However, there is; you can subclass
DetailView and provide your own
implementation of the get_context_data method. The default
implementation of this that comes with
DetailView simply adds in the
object being displayed to the template, but you can override it to show
more:
from django.views.generic import DetailView
from books.models import Publisher, Book
class PublisherDetailView(DetailView):
context_object_name = "publisher"
model = Publisher
def get_context_data(self, **kwargs):
# Call the base implementation first to get a context
context = super(PublisherDetailView, self).get_context_data(**kwargs)
# Add in a QuerySet of all the books
context['book_list'] = Book.objects.all()
return context
Now let’s take a closer look at the model argument we’ve been
using all along. The model argument, which specifies the database
model that the view will operate upon, is available on all the
generic views that operate on a single object or a collection of
objects. However, the model argument is not the only way to
specify the objects that the view will operate upon – you can also
specify the list of objects using the queryset argument:
from django.views.generic import DetailView
from books.models import Publisher, Book
class PublisherDetailView(DetailView):
context_object_name = "publisher"
queryset = Publisher.objects.all()
Specifying model = Publisher is really just shorthand for saying
queryset = Publisher.objects.all(). However, by using queryset
to define a filtered list of objects you can be more specific about the
objects that will be visible in the view (see Making queries
for more information about QuerySet objects, and see the
class-based views reference for the complete
details).
To pick a simple example, we might want to order a list of books by publication date, with the most recent first:
urlpatterns = patterns('',
(r'^publishers/$', ListView.as_view(
queryset=Publisher.objects.all(),
context_object_name="publisher_list",
)),
(r'^books/$', ListView.as_view(
queryset=Book.objects.order_by("-publication_date"),
context_object_name="book_list",
)),
)
That’s a pretty simple example, but it illustrates the idea nicely. Of course, you’ll usually want to do more than just reorder objects. If you want to present a list of books by a particular publisher, you can use the same technique (here, illustrated using subclassing rather than by passing arguments in the URLconf):
from django.views.generic import ListView
from books.models import Book
class AcmeBookListView(ListView):
context_object_name = "book_list"
queryset = Book.objects.filter(publisher__name="Acme Publishing")
template_name = "books/acme_list.html"
Notice that along with a filtered queryset, we’re also using a custom
template name. If we didn’t, the generic view would use the same template as the
“vanilla” object list, which might not be what we want.
Also notice that this isn’t a very elegant way of doing publisher-specific books. If we want to add another publisher page, we’d need another handful of lines in the URLconf, and more than a few publishers would get unreasonable. We’ll deal with this problem in the next section.
Note
If you get a 404 when requesting /books/acme/, check to ensure you
actually have a Publisher with the name ‘ACME Publishing’. Generic
views have an allow_empty parameter for this case. See the
class-based-views reference for more details.
Another common need is to filter down the objects given in a list page by some key in the URL. Earlier we hard-coded the publisher’s name in the URLconf, but what if we wanted to write a view that displayed all the books by some arbitrary publisher?
Handily, the ListView has a
get_queryset() method we can
override. Previously, it has just been returning the value of the queryset
attribute, but now we can add more logic.
The key part to making this work is that when class-based views are called,
various useful things are stored on self; as well as the request
(self.request) this includes the positional (self.args) and name-based
(self.kwargs) arguments captured according to the URLconf.
Here, we have a URLconf with a single captured group:
from books.views import PublisherBookListView
urlpatterns = patterns('',
(r'^books/(\w+)/$', PublisherBookListView.as_view()),
)
Next, we’ll write the PublisherBookListView view itself:
from django.shortcuts import get_object_or_404
from django.views.generic import ListView
from books.models import Book, Publisher
class PublisherBookListView(ListView):
context_object_name = "book_list"
template_name = "books/books_by_publisher.html"
def get_queryset(self):
publisher = get_object_or_404(Publisher, name__iexact=self.args[0])
return Book.objects.filter(publisher=publisher)
As you can see, it’s quite easy to add more logic to the queryset selection;
if we wanted, we could use self.request.user to filter using the current
user, or other more complex logic.
We can also add the publisher into the context at the same time, so we can use it in the template:
class PublisherBookListView(ListView):
context_object_name = "book_list"
template_name = "books/books_by_publisher.html"
def get_queryset(self):
self.publisher = get_object_or_404(Publisher, name__iexact=self.args[0])
return Book.objects.filter(publisher=self.publisher)
def get_context_data(self, **kwargs):
# Call the base implementation first to get a context
context = super(PublisherBookListView, self).get_context_data(**kwargs)
# Add in the publisher
context['publisher'] = self.publisher
return context
The last common pattern we’ll look at involves doing some extra work before or after calling the generic view.
Imagine we had a last_accessed field on our Author object that we were
using to keep track of the last time anybody looked at that author:
# models.py
class Author(models.Model):
salutation = models.CharField(max_length=10)
first_name = models.CharField(max_length=30)
last_name = models.CharField(max_length=40)
email = models.EmailField()
headshot = models.ImageField(upload_to='/tmp')
last_accessed = models.DateTimeField()
The generic DetailView class, of course, wouldn’t know anything about this
field, but once again we could easily write a custom view to keep that field
updated.
First, we’d need to add an author detail bit in the URLconf to point to a custom view:
from books.views import AuthorDetailView
urlpatterns = patterns('',
#...
(r'^authors/(?P<pk>\d+)/$', AuthorDetailView.as_view()),
)
Then we’d write our new view – get_object is the method that retrieves the
object – so we simply override it and wrap the call:
import datetime
from books.models import Author
from django.views.generic import DetailView
from django.shortcuts import get_object_or_404
class AuthorDetailView(DetailView):
queryset = Author.objects.all()
def get_object(self):
# Call the superclass
object = super(AuthorDetailView, self).get_object()
# Record the last accessed date
object.last_accessed = datetime.datetime.now()
object.save()
# Return the object
return object
Note
This code won’t actually work unless you create a
books/author_detail.html template.
Note
The URLconf here uses the named group pk - this name is the default
name that DetailView uses to find the value of the primary key used to
filter the queryset.
If you want to change it, you’ll need to do your own get() call
on self.queryset using the new named parameter from self.kwargs.
So far, we’ve been focusing on rendering templates to generate responses. However, that’s not all generic views can do.
Each generic view is composed out of a series of mixins, and each
mixin contributes a little piece of the entire view. Some of these
mixins – such as
TemplateResponseMixin – are
specifically designed for rendering content to an HTML response using a
template. However, you can write your own mixins that perform
different rendering behavior.
For example, a simple JSON mixin might look something like this:
from django import http
from django.utils import simplejson as json
class JSONResponseMixin(object):
def render_to_response(self, context):
"Returns a JSON response containing 'context' as payload"
return self.get_json_response(self.convert_context_to_json(context))
def get_json_response(self, content, **httpresponse_kwargs):
"Construct an `HttpResponse` object."
return http.HttpResponse(content,
content_type='application/json',
**httpresponse_kwargs)
def convert_context_to_json(self, context):
"Convert the context dictionary into a JSON object"
# Note: This is *EXTREMELY* naive; in reality, you'll need
# to do much more complex handling to ensure that arbitrary
# objects -- such as Django model instances or querysets
# -- can be serialized as JSON.
return json.dumps(context)
Then, you could build a JSON-returning
DetailView by mixing your
JSONResponseMixin with the
BaseDetailView – (the
DetailView before template
rendering behavior has been mixed in):
class JSONDetailView(JSONResponseMixin, BaseDetailView):
pass
This view can then be deployed in the same way as any other
DetailView, with exactly the
same behavior – except for the format of the response.
If you want to be really adventurous, you could even mix a
DetailView subclass that is able
to return both HTML and JSON content, depending on some property of
the HTTP request, such as a query argument or a HTTP header. Just mix
in both the JSONResponseMixin and a
SingleObjectTemplateResponseMixin,
and override the implementation of render_to_response() to defer
to the appropriate subclass depending on the type of response that the user
requested:
class HybridDetailView(JSONResponseMixin, SingleObjectTemplateResponseMixin, BaseDetailView):
def render_to_response(self, context):
# Look for a 'format=json' GET argument
if self.request.GET.get('format','html') == 'json':
return JSONResponseMixin.render_to_response(self, context)
else:
return SingleObjectTemplateResponseMixin.render_to_response(self, context)
Because of the way that Python resolves method overloading, the local
render_to_response() implementation will override the versions provided by
JSONResponseMixin and
SingleObjectTemplateResponseMixin.
The extension of class-based views isn’t limited to using mixins. You can use also use decorators.
The simplest way of decorating class-based views is to decorate the
result of the as_view() method.
The easiest place to do this is in the URLconf where you deploy your
view:
from django.contrib.auth.decorators import login_required, permission_required
from django.views.generic import TemplateView
from .views import VoteView
urlpatterns = patterns('',
(r'^about/', login_required(TemplateView.as_view(template_name="secret.html"))),
(r'^vote/', permission_required('polls.can_vote')(VoteView.as_view())),
)
This approach applies the decorator on a per-instance basis. If you want every instance of a view to be decorated, you need to take a different approach.
To decorate every instance of a class-based view, you need to decorate
the class definition itself. To do this you apply the decorator to the
dispatch() method of the class.
A method on a class isn’t quite the same as a standalone function, so
you can’t just apply a function decorator to the method – you need to
transform it into a method decorator first. The method_decorator
decorator transforms a function decorator into a method decorator so
that it can be used on an instance method. For example:
from django.contrib.auth.decorators import login_required
from django.utils.decorators import method_decorator
from django.views.generic import TemplateView
class ProtectedView(TemplateView):
template_name = 'secret.html'
@method_decorator(login_required)
def dispatch(self, *args, **kwargs):
return super(ProtectedView, self).dispatch(*args, **kwargs)
In this example, every instance of ProtectedView will have
login protection.
Note
method_decorator passes *args and **kwargs
as parameters to the decorated method on the class. If your method
does not accept a compatible set of parameters it will raise a
TypeError exception.
Nov 29, 2016