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Thanks Aymeric Augustin for shepherding the DEP and patch review. Thanks Marten Kenbeek and Tim Graham for contributing to the code. Thanks Tom Christie, Shai Berger, and Tim Graham for the docs.
132 lines
4.8 KiB
Plaintext
132 lines
4.8 KiB
Plaintext
=================
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Class-based views
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=================
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A view is a callable which takes a request and returns a
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response. This can be more than just a function, and Django provides
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an example of some classes which can be used as views. These allow you
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to structure your views and reuse code by harnessing inheritance and
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mixins. There are also some generic views for simple tasks which we'll
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get to later, but you may want to design your own structure of
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reusable views which suits your use case. For full details, see the
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:doc:`class-based views reference documentation</ref/class-based-views/index>`.
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.. toctree::
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:maxdepth: 1
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intro
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generic-display
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generic-editing
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mixins
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Basic examples
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==============
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Django provides base view classes which will suit a wide range of applications.
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All views inherit from the :class:`~django.views.generic.base.View` class, which
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handles linking the view in to the URLs, HTTP method dispatching and other
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simple features. :class:`~django.views.generic.base.RedirectView` is for a
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simple HTTP redirect, and :class:`~django.views.generic.base.TemplateView`
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extends the base class to make it also render a template.
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Simple usage in your URLconf
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============================
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The simplest way to use generic views is to create them directly in your
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URLconf. If you're only changing a few simple attributes on a class-based view,
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you can simply pass them into the
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:meth:`~django.views.generic.base.View.as_view` method call itself::
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from django.urls import path
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from django.views.generic import TemplateView
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urlpatterns = [
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path('about/', TemplateView.as_view(template_name="about.html")),
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]
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Any arguments passed to :meth:`~django.views.generic.base.View.as_view` will
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override attributes set on the class. In this example, we set ``template_name``
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on the ``TemplateView``. A similar overriding pattern can be used for the
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``url`` attribute on :class:`~django.views.generic.base.RedirectView`.
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Subclassing generic views
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=========================
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The second, more powerful way to use generic views is to inherit from an
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existing view and override attributes (such as the ``template_name``) or
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methods (such as ``get_context_data``) in your subclass to provide new values
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or methods. Consider, for example, a view that just displays one template,
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``about.html``. Django has a generic view to do this -
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:class:`~django.views.generic.base.TemplateView` - so we can just subclass it,
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and override the template name::
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# some_app/views.py
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from django.views.generic import TemplateView
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class AboutView(TemplateView):
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template_name = "about.html"
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Then we just need to add this new view into our URLconf.
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:class:`~django.views.generic.base.TemplateView` is a class, not a function,
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so we point the URL to the :meth:`~django.views.generic.base.View.as_view`
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class method instead, which provides a function-like entry to class-based
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views::
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# urls.py
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from django.urls import path
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from some_app.views import AboutView
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urlpatterns = [
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path('about/', AboutView.as_view()),
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]
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For more information on how to use the built in generic views, consult the next
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topic on :doc:`generic class-based views</topics/class-based-views/generic-display>`.
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.. _supporting-other-http-methods:
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Supporting other HTTP methods
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-----------------------------
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Suppose somebody wants to access our book library over HTTP using the views
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as an API. The API client would connect every now and then and download book
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data for the books published since last visit. But if no new books appeared
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since then, it is a waste of CPU time and bandwidth to fetch the books from the
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database, render a full response and send it to the client. It might be
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preferable to ask the API when the most recent book was published.
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We map the URL to book list view in the URLconf::
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from django.urls import path
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from books.views import BookListView
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urlpatterns = [
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path('books/', BookListView.as_view()),
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]
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And the view::
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from django.http import HttpResponse
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from django.views.generic import ListView
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from books.models import Book
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class BookListView(ListView):
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model = Book
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def head(self, *args, **kwargs):
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last_book = self.get_queryset().latest('publication_date')
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response = HttpResponse('')
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# RFC 1123 date format
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response['Last-Modified'] = last_book.publication_date.strftime('%a, %d %b %Y %H:%M:%S GMT')
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return response
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If the view is accessed from a ``GET`` request, a plain-and-simple object
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list is returned in the response (using ``book_list.html`` template). But if
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the client issues a ``HEAD`` request, the response has an empty body and
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the ``Last-Modified`` header indicates when the most recent book was published.
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Based on this information, the client may or may not download the full object
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list.
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