<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Generic views — Django 1.4.21 documentation</title> <link rel="stylesheet" href="../_static/default.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript"> var DOCUMENTATION_OPTIONS = { URL_ROOT: '../', VERSION: '1.4.21', COLLAPSE_INDEX: false, FILE_SUFFIX: '.html', HAS_SOURCE: true }; </script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <link rel="top" title="Django 1.4.21 documentation" href="../index.html" /> <link rel="up" title="Using Django" href="index.html" /> <link rel="next" title="“How-to” guides" href="../howto/index.html" /> <link rel="prev" title="Signals" href="signals.html" /> <script type="text/javascript" src="../templatebuiltins.js"></script> <script type="text/javascript"> (function($) { if (!django_template_builtins) { // templatebuiltins.js missing, do nothing. return; } $(document).ready(function() { // Hyperlink Django template tags and filters var base = "../ref/templates/builtins.html"; if (base == "#") { // Special case for builtins.html itself base = ""; } // Tags are keywords, class '.k' $("div.highlight\\-html\\+django span.k").each(function(i, elem) { var tagname = $(elem).text(); if ($.inArray(tagname, django_template_builtins.ttags) != -1) { var fragment = tagname.replace(/_/, '-'); $(elem).html("<a href='" + base + "#" + fragment + "'>" + tagname + "</a>"); } }); // Filters are functions, class '.nf' $("div.highlight\\-html\\+django span.nf").each(function(i, elem) { var filtername = $(elem).text(); if ($.inArray(filtername, django_template_builtins.tfilters) != -1) { var fragment = filtername.replace(/_/, '-'); $(elem).html("<a href='" + base + "#" + fragment + "'>" + filtername + "</a>"); } }); }); })(jQuery); </script> </head> <body> <div class="document"> <div id="custom-doc" class="yui-t6"> <div id="hd"> <h1><a href="../index.html">Django 1.4.21 documentation</a></h1> <div id="global-nav"> <a title="Home page" href="../index.html">Home</a> | <a title="Table of contents" href="../contents.html">Table of contents</a> | <a title="Global index" href="../genindex.html">Index</a> | <a title="Module index" href="../py-modindex.html">Modules</a> </div> <div class="nav"> « <a href="signals.html" title="Signals">previous</a> | <a href="index.html" title="Using Django" accesskey="U">up</a> | <a href="../howto/index.html" title="&#8220;How-to&#8221; guides">next</a> »</div> </div> <div id="bd"> <div id="yui-main"> <div class="yui-b"> <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> <div class="versionchanged"> <span class="title">Changed in Django 1.3:</span> <a class="reference internal" href="../releases/1.3.html"><em>Please see the release notes</em></a></div> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">From Django 1.3, function-based generic views have been deprecated in favor of a class-based approach, described in the class-based views <a class="reference internal" href="class-based-views.html"><em>topic guide</em></a> and <a class="reference internal" href="../ref/class-based-views.html"><em>detailed reference</em></a>.</p> </div> <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="https://www.djangoproject.com/weblog/">https://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</span> <span class="kn">import</span> <span class="n">patterns</span><span class="p">,</span> <span class="n">url</span><span class="p">,</span> <span class="n">include</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 import patterns, url, include from django.views.generic.simple import direct_to_template <strong>from 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</span> <span class="kn">import</span> <span class="n">patterns</span><span class="p">,</span> <span class="n">url</span><span class="p">,</span> <span class="n">include</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">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 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 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">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 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">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> </div> </div> </div> <div class="yui-b" id="sidebar"> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <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> <h3>Browse</h3> <ul> <li>Prev: <a href="signals.html">Signals</a></li> <li>Next: <a href="../howto/index.html">“How-to” guides</a></li> </ul> <h3>You are here:</h3> <ul> <li> <a href="../index.html">Django 1.4.21 documentation</a> <ul><li><a href="index.html">Using Django</a> <ul><li>Generic views</li></ul> </li></ul> </li> </ul> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../_sources/topics/generic-views.txt" rel="nofollow">Show Source</a></li> </ul> <div id="searchbox" style="display: none"> <h3>Quick search</h3> <form class="search" action="../search.html" method="get"> <input type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> <p class="searchtip" style="font-size: 90%"> Enter search terms or a module, class or function name. </p> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </div> </div> <h3>Last update:</h3> <p class="topless">Jul 10, 2015</p> </div> </div> <div id="ft"> <div class="nav"> « <a href="signals.html" title="Signals">previous</a> | <a href="index.html" title="Using Django" accesskey="U">up</a> | <a href="../howto/index.html" title="&#8220;How-to&#8221; guides">next</a> »</div> </div> </div> <div class="clearer"></div> </div> </body> </html>