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<div class="yui-g" id="topics-generic-views">
<div class="section" id="s-generic-views">
<span id="generic-views"></span><h1>Generic views<a class="headerlink" href="#generic-views" title="Permalink to this headline">¶</a></h1>
<p>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.</p>
<p>Django’s <em>generic views</em> 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.</p>
<p>We can recognize certain common tasks, like displaying a list of objects, and
write code that displays a list of <em>any</em> object. Then the model in question can
be passed as an extra argument to the URLconf.</p>
<p>Django ships with generic views to do the following:</p>
<ul class="simple">
<li>Perform common “simple” tasks: redirect to a different page and
render a given template.</li>
<li>Display list and detail pages for a single object. If we were creating an
application to manage conferences then a <tt class="docutils literal"><span class="pre">talk_list</span></tt> view and a
<tt class="docutils literal"><span class="pre">registered_user_list</span></tt> view would be examples of list views. A single
talk page is an example of what we call a “detail” view.</li>
<li>Present date-based objects in year/month/day archive pages,
associated detail, and “latest” pages. The Django Weblog’s
(<a class="reference external" href="http://www.djangoproject.com/weblog/">http://www.djangoproject.com/weblog/</a>) year, month, and
day archives are built with these, as would be a typical
newspaper’s archives.</li>
<li>Allow users to create, update, and delete objects – with or
without authorization.</li>
</ul>
<p>Taken together, these views provide easy interfaces to perform the most common
tasks developers encounter.</p>
<div class="section" id="s-using-generic-views">
<span id="using-generic-views"></span><h2>Using generic views<a class="headerlink" href="#using-generic-views" title="Permalink to this headline">¶</a></h2>
<p>All of these views are used by creating configuration dictionaries in
your URLconf files and passing those dictionaries as the third member of the
URLconf tuple for a given pattern.</p>
<p>For example, here’s a simple URLconf you could use to present a static “about”
page:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">django.conf.urls.defaults</span> <span class="kn">import</span> <span class="o">*</span>
<span class="kn">from</span> <span class="nn">django.views.generic.simple</span> <span class="kn">import</span> <span class="n">direct_to_template</span>
<span class="n">urlpatterns</span> <span class="o">=</span> <span class="n">patterns</span><span class="p">(</span><span class="s">''</span><span class="p">,</span>
<span class="p">(</span><span class="s">'^about/$'</span><span class="p">,</span> <span class="n">direct_to_template</span><span class="p">,</span> <span class="p">{</span>
<span class="s">'template'</span><span class="p">:</span> <span class="s">'about.html'</span>
<span class="p">})</span>
<span class="p">)</span>
</pre></div>
</div>
<p>Though this might seem a bit "magical" at first glance -- look, a view with no
code! --, actually the <tt class="docutils literal"><span class="pre">direct_to_template</span></tt> view simply grabs information from
the extra-parameters dictionary and uses that information when rendering the
view.</p>
<p>Because this generic view -- and all the others -- is a regular view function
like any other, we can reuse it inside our own views. As an example, let's
extend our "about" example to map URLs of the form <tt class="docutils literal"><span class="pre">/about/<whatever>/</span></tt> to
statically rendered <tt class="docutils literal"><span class="pre">about/<whatever>.html</span></tt>. We'll do this by first modifying
the URLconf to point to a view function:</p>
<pre class="literal-block">
from django.conf.urls.defaults import *
from django.views.generic.simple import direct_to_template
<strong>from mysite.books.views import about_pages</strong>
urlpatterns = patterns('',
('^about/$', direct_to_template, {
'template': 'about.html'
}),
<strong>('^about/(\w+)/$', about_pages),</strong>
)
</pre>
<p>Next, we'll write the <tt class="docutils literal"><span class="pre">about_pages</span></tt> view:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">django.http</span> <span class="kn">import</span> <span class="n">Http404</span>
<span class="kn">from</span> <span class="nn">django.template</span> <span class="kn">import</span> <span class="n">TemplateDoesNotExist</span>
<span class="kn">from</span> <span class="nn">django.views.generic.simple</span> <span class="kn">import</span> <span class="n">direct_to_template</span>
<span class="k">def</span> <span class="nf">about_pages</span><span class="p">(</span><span class="n">request</span><span class="p">,</span> <span class="n">page</span><span class="p">):</span>
<span class="k">try</span><span class="p">:</span>
<span class="k">return</span> <span class="n">direct_to_template</span><span class="p">(</span><span class="n">request</span><span class="p">,</span> <span class="n">template</span><span class="o">=</span><span class="s">"about/</span><span class="si">%s</span><span class="s">.html"</span> <span class="o">%</span> <span class="n">page</span><span class="p">)</span>
<span class="k">except</span> <span class="n">TemplateDoesNotExist</span><span class="p">:</span>
<span class="k">raise</span> <span class="n">Http404</span><span class="p">()</span>
</pre></div>
</div>
<p>Here we're treating <tt class="docutils literal"><span class="pre">direct_to_template</span></tt> like any other function. Since it
returns an <tt class="docutils literal"><span class="pre">HttpResponse</span></tt>, we can simply return it as-is. The only slightly
tricky business here is dealing with missing templates. We don't want a
nonexistent template to cause a server error, so we catch
<tt class="docutils literal"><span class="pre">TemplateDoesNotExist</span></tt> exceptions and return 404 errors instead.</p>
<div class="admonition-is-there-a-security-vulnerability-here admonition ">
<p class="first admonition-title">Is there a security vulnerability here?</p>
<p>Sharp-eyed readers may have noticed a possible security hole: we're
constructing the template name using interpolated content from the browser
(<tt class="docutils literal"><span class="pre">template="about/%s.html"</span> <span class="pre">%</span> <span class="pre">page</span></tt>). At first glance, this looks like a
classic <em>directory traversal</em> vulnerability. But is it really?</p>
<p class="last">Not exactly. Yes, a maliciously crafted value of <tt class="docutils literal"><span class="pre">page</span></tt> could cause
directory traversal, but although <tt class="docutils literal"><span class="pre">page</span></tt> <em>is</em> taken from the request URL,
not every value will be accepted. The key is in the URLconf: we're using
the regular expression <tt class="docutils literal"><span class="pre">\w+</span></tt> to match the <tt class="docutils literal"><span class="pre">page</span></tt> part of the URL, and
<tt class="docutils literal"><span class="pre">\w</span></tt> only accepts letters and numbers. Thus, any malicious characters
(dots and slashes, here) will be rejected by the URL resolver before they
reach the view itself.</p>
</div>
</div>
<div class="section" id="s-generic-views-of-objects">
<span id="generic-views-of-objects"></span><h2>Generic views of objects<a class="headerlink" href="#generic-views-of-objects" title="Permalink to this headline">¶</a></h2>
<p>The <tt class="docutils literal"><span class="pre">direct_to_template</span></tt> certainly is useful, but Django's generic views
really shine when it comes to presenting views on 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.</p>
<p>Let's take a look at one of these generic views: the "object list" view. We'll
be using these models:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c"># models.py</span>
<span class="kn">from</span> <span class="nn">django.db</span> <span class="kn">import</span> <span class="n">models</span>
<span class="k">class</span> <span class="nc">Publisher</span><span class="p">(</span><span class="n">models</span><span class="o">.</span><span class="n">Model</span><span class="p">):</span>
<span class="n">name</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">30</span><span class="p">)</span>
<span class="n">address</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">50</span><span class="p">)</span>
<span class="n">city</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">60</span><span class="p">)</span>
<span class="n">state_province</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">30</span><span class="p">)</span>
<span class="n">country</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">50</span><span class="p">)</span>
<span class="n">website</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">URLField</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">__unicode__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">name</span>
<span class="k">class</span> <span class="nc">Meta</span><span class="p">:</span>
<span class="n">ordering</span> <span class="o">=</span> <span class="p">[</span><span class="s">"-name"</span><span class="p">]</span>
<span class="k">class</span> <span class="nc">Book</span><span class="p">(</span><span class="n">models</span><span class="o">.</span><span class="n">Model</span><span class="p">):</span>
<span class="n">title</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">100</span><span class="p">)</span>
<span class="n">authors</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">ManyToManyField</span><span class="p">(</span><span class="s">'Author'</span><span class="p">)</span>
<span class="n">publisher</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">ForeignKey</span><span class="p">(</span><span class="n">Publisher</span><span class="p">)</span>
<span class="n">publication_date</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">DateField</span><span class="p">()</span>
</pre></div>
</div>
<p>To build a list page of all publishers, we'd use a URLconf along these lines:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">django.conf.urls.defaults</span> <span class="kn">import</span> <span class="o">*</span>
<span class="kn">from</span> <span class="nn">django.views.generic</span> <span class="kn">import</span> <span class="n">list_detail</span>
<span class="kn">from</span> <span class="nn">mysite.books.models</span> <span class="kn">import</span> <span class="n">Publisher</span>
<span class="n">publisher_info</span> <span class="o">=</span> <span class="p">{</span>
<span class="s">"queryset"</span> <span class="p">:</span> <span class="n">Publisher</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">all</span><span class="p">(),</span>
<span class="p">}</span>
<span class="n">urlpatterns</span> <span class="o">=</span> <span class="n">patterns</span><span class="p">(</span><span class="s">''</span><span class="p">,</span>
<span class="p">(</span><span class="s">r'^publishers/$'</span><span class="p">,</span> <span class="n">list_detail</span><span class="o">.</span><span class="n">object_list</span><span class="p">,</span> <span class="n">publisher_info</span><span class="p">)</span>
<span class="p">)</span>
</pre></div>
</div>
<p>That's all the Python code we need to write. We still need to write a template,
however. We could explicitly tell the <tt class="docutils literal"><span class="pre">object_list</span></tt> view which template to use
by including a <tt class="docutils literal"><span class="pre">template_name</span></tt> key in the extra arguments dictionary, 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
<tt class="docutils literal"><span class="pre">"books/publisher_list.html"</span></tt> -- 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.</p>
<p>This template will be rendered against a context containing a variable called
<tt class="docutils literal"><span class="pre">object_list</span></tt> that contains all the publisher objects. A very simple template
might look like the following:</p>
<div class="highlight-html+django"><div class="highlight"><pre><span class="cp">{%</span> <span class="k">extends</span> <span class="s2">"base.html"</span> <span class="cp">%}</span>
<span class="cp">{%</span> <span class="k">block</span> <span class="nv">content</span> <span class="cp">%}</span>
<span class="nt"><h2></span>Publishers<span class="nt"></h2></span>
<span class="nt"><ul></span>
<span class="cp">{%</span> <span class="k">for</span> <span class="nv">publisher</span> <span class="k">in</span> <span class="nv">object_list</span> <span class="cp">%}</span>
<span class="nt"><li></span><span class="cp">{{</span> <span class="nv">publisher.name</span> <span class="cp">}}</span><span class="nt"></li></span>
<span class="cp">{%</span> <span class="k">endfor</span> <span class="cp">%}</span>
<span class="nt"></ul></span>
<span class="cp">{%</span> <span class="k">endblock</span> <span class="cp">%}</span>
</pre></div>
</div>
<p>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
<a class="reference internal" href="../ref/generic-views.html"><em>generic views reference</em></a> documents all the generic
views and all their options in detail; the rest of this document will consider
some of the common ways you might customize and extend generic views.</p>
</div>
<div class="section" id="s-extending-generic-views">
<span id="extending-generic-views"></span><h2>Extending generic views<a class="headerlink" href="#extending-generic-views" title="Permalink to this headline">¶</a></h2>
<p>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.</p>
<p>Luckily, in nearly every one of these cases, there are ways to simply extend
generic views to handle a larger array of use cases. These situations usually
fall into a handful of patterns dealt with in the sections that follow.</p>
<div class="section" id="s-making-friendly-template-contexts">
<span id="making-friendly-template-contexts"></span><h3>Making "friendly" template contexts<a class="headerlink" href="#making-friendly-template-contexts" title="Permalink to this headline">¶</a></h3>
<p>You might have noticed that our sample publisher list template stores all the
books in a variable named <tt class="docutils literal"><span class="pre">object_list</span></tt>. 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. A better name for that variable would be
<tt class="docutils literal"><span class="pre">publisher_list</span></tt>; that variable's content is pretty obvious.</p>
<p>We can change the name of that variable easily with the <tt class="docutils literal"><span class="pre">template_object_name</span></tt>
argument:</p>
<pre class="literal-block">
publisher_info = {
"queryset" : Publisher.objects.all(),
<strong>"template_object_name" : "publisher",</strong>
}
urlpatterns = patterns('',
(r'^publishers/$', list_detail.object_list, publisher_info)
)
</pre>
<p>Providing a useful <tt class="docutils literal"><span class="pre">template_object_name</span></tt> is always a good idea. Your
coworkers who design templates will thank you.</p>
</div>
<div class="section" id="s-adding-extra-context">
<span id="adding-extra-context"></span><h3>Adding extra context<a class="headerlink" href="#adding-extra-context" title="Permalink to this headline">¶</a></h3>
<p>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 <tt class="docutils literal"><span class="pre">object_detail</span></tt> generic view provides the
publisher to the context, but it seems there's no way to get additional
information in that template.</p>
<p>But there is: all generic views take an extra optional parameter,
<tt class="docutils literal"><span class="pre">extra_context</span></tt>. This is a dictionary of extra objects that will be added to
the template's context. So, to provide the list of all books on the detail
detail view, we'd use an info dict like this:</p>
<pre class="literal-block">
from mysite.books.models import Publisher, <strong>Book</strong>
publisher_info = {
"queryset" : Publisher.objects.all(),
"template_object_name" : "publisher",
<strong>"extra_context" : {"book_list" : Book.objects.all()}</strong>
}
</pre>
<p>This would populate a <tt class="docutils literal"><span class="pre">{{</span> <span class="pre">book_list</span> <span class="pre">}}</span></tt> variable in the template context.
This pattern can be used to pass any information down into the template for the
generic view. It's very handy.</p>
<p>However, there's actually a subtle bug here -- can you spot it?</p>
<p>The problem has to do with when the queries in <tt class="docutils literal"><span class="pre">extra_context</span></tt> are evaluated.
Because this example puts <tt class="docutils literal"><span class="pre">Book.objects.all()</span></tt> in the URLconf, it will
be evaluated only once (when the URLconf is first loaded). Once you add or
remove books, you'll notice that the generic view doesn't reflect those
changes until you reload the Web server (see <a class="reference internal" href="db/queries.html#caching-and-querysets"><em>Caching and QuerySets</em></a>
for more information about when QuerySets are cached and evaluated).</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">This problem doesn't apply to the <tt class="docutils literal"><span class="pre">queryset</span></tt> generic view argument. Since
Django knows that particular QuerySet should <em>never</em> be cached, the generic
view takes care of clearing the cache when each view is rendered.</p>
</div>
<p>The solution is to use a callback in <tt class="docutils literal"><span class="pre">extra_context</span></tt> instead of a value. Any
callable (i.e., a function) that's passed to <tt class="docutils literal"><span class="pre">extra_context</span></tt> will be evaluated
when the view is rendered (instead of only once). You could do this with an
explicitly defined function:</p>
<pre class="literal-block">
def get_books():
return Book.objects.all()
publisher_info = {
"queryset" : Publisher.objects.all(),
"template_object_name" : "publisher",
"extra_context" : <strong>{"book_list" : get_books}</strong>
}
</pre>
<p>or you could use a less obvious but shorter version that relies on the fact that
<tt class="docutils literal"><span class="pre">Book.objects.all</span></tt> is itself a callable:</p>
<pre class="literal-block">
publisher_info = {
"queryset" : Publisher.objects.all(),
"template_object_name" : "publisher",
"extra_context" : <strong>{"book_list" : Book.objects.all}</strong>
}
</pre>
<p>Notice the lack of parentheses after <tt class="docutils literal"><span class="pre">Book.objects.all</span></tt>; this references
the function without actually calling it (which the generic view will do later).</p>
</div>
<div class="section" id="s-viewing-subsets-of-objects">
<span id="viewing-subsets-of-objects"></span><h3>Viewing subsets of objects<a class="headerlink" href="#viewing-subsets-of-objects" title="Permalink to this headline">¶</a></h3>
<p>Now let's take a closer look at this <tt class="docutils literal"><span class="pre">queryset</span></tt> key we've been using all
along. Most generic views take one of these <tt class="docutils literal"><span class="pre">queryset</span></tt> arguments -- it's how
the view knows which set of objects to display (see <a class="reference internal" href="db/queries.html"><em>Making queries</em></a> for
more information about <tt class="docutils literal"><span class="pre">QuerySet</span></tt> objects, and see the
<a class="reference internal" href="../ref/generic-views.html"><em>generic views reference</em></a> for the complete details).</p>
<p>To pick a simple example, we might want to order a list of books by
publication date, with the most recent first:</p>
<pre class="literal-block">
book_info = {
"queryset" : Book.objects.all().order_by("-publication_date"),
}
urlpatterns = patterns('',
(r'^publishers/$', list_detail.object_list, publisher_info),
<strong>(r'^books/$', list_detail.object_list, book_info),</strong>
)
</pre>
<p>That's a pretty simple example, but it illustrates the idea nicely. Of course,
you'll usually want to do more than just reorder objects. If you want to
present a list of books by a particular publisher, you can use the same
technique:</p>
<pre class="literal-block">
<strong>acme_books = {</strong>
<strong>"queryset": Book.objects.filter(publisher__name="Acme Publishing"),</strong>
<strong>"template_name" : "books/acme_list.html"</strong>
<strong>}</strong>
urlpatterns = patterns('',
(r'^publishers/$', list_detail.object_list, publisher_info),
<strong>(r'^books/acme/$', list_detail.object_list, acme_books),</strong>
)
</pre>
<p>Notice that along with a filtered <tt class="docutils literal"><span class="pre">queryset</span></tt>, 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.</p>
<p>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.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">If you get a 404 when requesting <tt class="docutils literal"><span class="pre">/books/acme/</span></tt>, check to ensure you
actually have a Publisher with the name 'ACME Publishing'. Generic
views have an <tt class="docutils literal"><span class="pre">allow_empty</span></tt> parameter for this case. See the
<a class="reference internal" href="../ref/generic-views.html"><em>generic views reference</em></a> for more details.</p>
</div>
</div>
<div class="section" id="s-complex-filtering-with-wrapper-functions">
<span id="complex-filtering-with-wrapper-functions"></span><h3>Complex filtering with wrapper functions<a class="headerlink" href="#complex-filtering-with-wrapper-functions" title="Permalink to this headline">¶</a></h3>
<p>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? We can "wrap" the <tt class="docutils literal"><span class="pre">object_list</span></tt> generic view to avoid writing a lot
of code by hand. As usual, we'll start by writing a URLconf:</p>
<pre class="literal-block">
from mysite.books.views import books_by_publisher
urlpatterns = patterns('',
(r'^publishers/$', list_detail.object_list, publisher_info),
<strong>(r'^books/(\w+)/$', books_by_publisher),</strong>
)
</pre>
<p>Next, we'll write the <tt class="docutils literal"><span class="pre">books_by_publisher</span></tt> view itself:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">django.http</span> <span class="kn">import</span> <span class="n">Http404</span>
<span class="kn">from</span> <span class="nn">django.views.generic</span> <span class="kn">import</span> <span class="n">list_detail</span>
<span class="kn">from</span> <span class="nn">mysite.books.models</span> <span class="kn">import</span> <span class="n">Book</span><span class="p">,</span> <span class="n">Publisher</span>
<span class="k">def</span> <span class="nf">books_by_publisher</span><span class="p">(</span><span class="n">request</span><span class="p">,</span> <span class="n">name</span><span class="p">):</span>
<span class="c"># Look up the publisher (and raise a 404 if it can't be found).</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">publisher</span> <span class="o">=</span> <span class="n">Publisher</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="n">name__iexact</span><span class="o">=</span><span class="n">name</span><span class="p">)</span>
<span class="k">except</span> <span class="n">Publisher</span><span class="o">.</span><span class="n">DoesNotExist</span><span class="p">:</span>
<span class="k">raise</span> <span class="n">Http404</span>
<span class="c"># Use the object_list view for the heavy lifting.</span>
<span class="k">return</span> <span class="n">list_detail</span><span class="o">.</span><span class="n">object_list</span><span class="p">(</span>
<span class="n">request</span><span class="p">,</span>
<span class="n">queryset</span> <span class="o">=</span> <span class="n">Book</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">filter</span><span class="p">(</span><span class="n">publisher</span><span class="o">=</span><span class="n">publisher</span><span class="p">),</span>
<span class="n">template_name</span> <span class="o">=</span> <span class="s">"books/books_by_publisher.html"</span><span class="p">,</span>
<span class="n">template_object_name</span> <span class="o">=</span> <span class="s">"books"</span><span class="p">,</span>
<span class="n">extra_context</span> <span class="o">=</span> <span class="p">{</span><span class="s">"publisher"</span> <span class="p">:</span> <span class="n">publisher</span><span class="p">}</span>
<span class="p">)</span>
</pre></div>
</div>
<p>This works because there's really nothing special about generic views -- they're
just Python functions. Like any view function, generic views expect a certain
set of arguments and return <tt class="docutils literal"><span class="pre">HttpResponse</span></tt> objects. Thus, it's incredibly easy
to wrap a small function around a generic view that does additional work before
(or after; see the next section) handing things off to the generic view.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Notice that in the preceding example we passed the current publisher being
displayed in the <tt class="docutils literal"><span class="pre">extra_context</span></tt>. This is usually a good idea in wrappers
of this nature; it lets the template know which "parent" object is currently
being browsed.</p>
</div>
</div>
<div class="section" id="s-performing-extra-work">
<span id="performing-extra-work"></span><h3>Performing extra work<a class="headerlink" href="#performing-extra-work" title="Permalink to this headline">¶</a></h3>
<p>The last common pattern we'll look at involves doing some extra work before
or after calling the generic view.</p>
<p>Imagine we had a <tt class="docutils literal"><span class="pre">last_accessed</span></tt> field on our <tt class="docutils literal"><span class="pre">Author</span></tt> object that we were
using to keep track of the last time anybody looked at that author:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c"># models.py</span>
<span class="k">class</span> <span class="nc">Author</span><span class="p">(</span><span class="n">models</span><span class="o">.</span><span class="n">Model</span><span class="p">):</span>
<span class="n">salutation</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">10</span><span class="p">)</span>
<span class="n">first_name</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">30</span><span class="p">)</span>
<span class="n">last_name</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">CharField</span><span class="p">(</span><span class="n">max_length</span><span class="o">=</span><span class="mi">40</span><span class="p">)</span>
<span class="n">email</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">EmailField</span><span class="p">()</span>
<span class="n">headshot</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">ImageField</span><span class="p">(</span><span class="n">upload_to</span><span class="o">=</span><span class="s">'/tmp'</span><span class="p">)</span>
<span class="n">last_accessed</span> <span class="o">=</span> <span class="n">models</span><span class="o">.</span><span class="n">DateTimeField</span><span class="p">()</span>
</pre></div>
</div>
<p>The generic <tt class="docutils literal"><span class="pre">object_detail</span></tt> view, of course, wouldn't know anything about this
field, but once again we could easily write a custom view to keep that field
updated.</p>
<p>First, we'd need to add an author detail bit in the URLconf to point to a
custom view:</p>
<pre class="literal-block">
from mysite.books.views import author_detail
urlpatterns = patterns('',
#...
<strong>(r'^authors/(?P<author_id>\d+)/$', author_detail),</strong>
)
</pre>
<p>Then we'd write our wrapper function:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">datetime</span>
<span class="kn">from</span> <span class="nn">mysite.books.models</span> <span class="kn">import</span> <span class="n">Author</span>
<span class="kn">from</span> <span class="nn">django.views.generic</span> <span class="kn">import</span> <span class="n">list_detail</span>
<span class="kn">from</span> <span class="nn">django.shortcuts</span> <span class="kn">import</span> <span class="n">get_object_or_404</span>
<span class="k">def</span> <span class="nf">author_detail</span><span class="p">(</span><span class="n">request</span><span class="p">,</span> <span class="n">author_id</span><span class="p">):</span>
<span class="c"># Look up the Author (and raise a 404 if she's not found)</span>
<span class="n">author</span> <span class="o">=</span> <span class="n">get_object_or_404</span><span class="p">(</span><span class="n">Author</span><span class="p">,</span> <span class="n">pk</span><span class="o">=</span><span class="n">author_id</span><span class="p">)</span>
<span class="c"># Record the last accessed date</span>
<span class="n">author</span><span class="o">.</span><span class="n">last_accessed</span> <span class="o">=</span> <span class="n">datetime</span><span class="o">.</span><span class="n">datetime</span><span class="o">.</span><span class="n">now</span><span class="p">()</span>
<span class="n">author</span><span class="o">.</span><span class="n">save</span><span class="p">()</span>
<span class="c"># Show the detail page</span>
<span class="k">return</span> <span class="n">list_detail</span><span class="o">.</span><span class="n">object_detail</span><span class="p">(</span>
<span class="n">request</span><span class="p">,</span>
<span class="n">queryset</span> <span class="o">=</span> <span class="n">Author</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">all</span><span class="p">(),</span>
<span class="n">object_id</span> <span class="o">=</span> <span class="n">author_id</span><span class="p">,</span>
<span class="p">)</span>
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">This code won't actually work unless you create a
<tt class="docutils literal"><span class="pre">books/author_detail.html</span></tt> template.</p>
</div>
<p>We can use a similar idiom to alter the response returned by the generic view.
If we wanted to provide a downloadable plain-text version of the list of
authors, we could use a view like this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">author_list_plaintext</span><span class="p">(</span><span class="n">request</span><span class="p">):</span>
<span class="n">response</span> <span class="o">=</span> <span class="n">list_detail</span><span class="o">.</span><span class="n">object_list</span><span class="p">(</span>
<span class="n">request</span><span class="p">,</span>
<span class="n">queryset</span> <span class="o">=</span> <span class="n">Author</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">all</span><span class="p">(),</span>
<span class="n">mimetype</span> <span class="o">=</span> <span class="s">"text/plain"</span><span class="p">,</span>
<span class="n">template_name</span> <span class="o">=</span> <span class="s">"books/author_list.txt"</span>
<span class="p">)</span>
<span class="n">response</span><span class="p">[</span><span class="s">"Content-Disposition"</span><span class="p">]</span> <span class="o">=</span> <span class="s">"attachment; filename=authors.txt"</span>
<span class="k">return</span> <span class="n">response</span>
</pre></div>
</div>
<p>This works because the generic views return simple <tt class="docutils literal"><span class="pre">HttpResponse</span></tt> objects
that can be treated like dictionaries to set HTTP headers. This
<tt class="docutils literal"><span class="pre">Content-Disposition</span></tt> business, by the way, instructs the browser to
download and save the page instead of displaying it in the browser.</p>
</div>
</div>
</div>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Generic views</a><ul>
<li><a class="reference internal" href="#using-generic-views">Using generic views</a></li>
<li><a class="reference internal" href="#generic-views-of-objects">Generic views of objects</a></li>
<li><a class="reference internal" href="#extending-generic-views">Extending generic views</a><ul>
<li><a class="reference internal" href="#making-friendly-template-contexts">Making “friendly” template contexts</a></li>
<li><a class="reference internal" href="#adding-extra-context">Adding extra context</a></li>
<li><a class="reference internal" href="#viewing-subsets-of-objects">Viewing subsets of objects</a></li>
<li><a class="reference internal" href="#complex-filtering-with-wrapper-functions">Complex filtering with wrapper functions</a></li>
<li><a class="reference internal" href="#performing-extra-work">Performing extra work</a></li>
</ul>
</li>
</ul>
</li>
</ul>
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