<!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>Related objects reference — Django 1.5.8 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: '1.5.8', 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 1.5.8 documentation" href="../../index.html" /> <link rel="up" title="Models" href="index.html" /> <link rel="next" title="Model Meta options" href="options.html" /> <link rel="prev" title="Model field reference" href="fields.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 = "../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 1.5.8 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="fields.html" title="Model field reference">previous</a> | <a href="../index.html" title="API Reference" accesskey="U">up</a> | <a href="options.html" title="Model <tt class="docutils literal"><span class="pre">Meta</span></tt> options">next</a> »</div> </div> <div id="bd"> <div id="yui-main"> <div class="yui-b"> <div class="yui-g" id="ref-models-relations"> <div class="section" id="s-related-objects-reference"> <span id="related-objects-reference"></span><h1>Related objects reference<a class="headerlink" href="#related-objects-reference" title="Permalink to this headline">¶</a></h1> <dl class="class"> <dt id="django.db.models.fields.related.RelatedManager"> <em class="property">class </em><tt class="descname">RelatedManager</tt><a class="headerlink" href="#django.db.models.fields.related.RelatedManager" title="Permalink to this definition">¶</a></dt> <dd><p>A “related manager” is a manager used in a one-to-many or many-to-many related context. This happens in two cases:</p> <ul> <li><p class="first">The “other side” of a <a class="reference internal" href="fields.html#django.db.models.ForeignKey" title="django.db.models.ForeignKey"><tt class="xref py py-class docutils literal"><span class="pre">ForeignKey</span></tt></a> relation. That is:</p> <div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">Reporter</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="o">...</span> <span class="k">class</span> <span class="nc">Article</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">reporter</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">Reporter</span><span class="p">)</span> </pre></div> </div> <p>In the above example, the methods below will be available on the manager <tt class="docutils literal"><span class="pre">reporter.article_set</span></tt>.</p> </li> <li><p class="first">Both sides of a <a class="reference internal" href="fields.html#django.db.models.ManyToManyField" title="django.db.models.ManyToManyField"><tt class="xref py py-class docutils literal"><span class="pre">ManyToManyField</span></tt></a> relation:</p> <div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">Topping</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="o">...</span> <span class="k">class</span> <span class="nc">Pizza</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">toppings</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="n">Topping</span><span class="p">)</span> </pre></div> </div> <p>In this example, the methods below will be available both on <tt class="docutils literal"><span class="pre">topping.pizza_set</span></tt> and on <tt class="docutils literal"><span class="pre">pizza.toppings</span></tt>.</p> </li> </ul> <p>These related managers have some extra methods:</p> <dl class="method"> <dt id="django.db.models.fields.related.RelatedManager.add"> <tt class="descname">add</tt>(<em>obj1</em><span class="optional">[</span>, <em>obj2</em>, <em>...</em><span class="optional">]</span>)<a class="headerlink" href="#django.db.models.fields.related.RelatedManager.add" title="Permalink to this definition">¶</a></dt> <dd><p>Adds the specified model objects to the related object set.</p> <p>Example:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">b</span> <span class="o">=</span> <span class="n">Blog</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="nb">id</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">e</span> <span class="o">=</span> <span class="n">Entry</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="nb">id</span><span class="o">=</span><span class="mi">234</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">b</span><span class="o">.</span><span class="n">entry_set</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">e</span><span class="p">)</span> <span class="c"># Associates Entry e with Blog b.</span> </pre></div> </div> <p>In the example above, <tt class="docutils literal"><span class="pre">e.save()</span></tt> is called to perform the update. Using <tt class="docutils literal"><span class="pre">add()</span></tt> with a many-to-many relationship, however, will not call any <tt class="docutils literal"><span class="pre">save()</span></tt> methods, but rather create the relationships using <a class="reference internal" href="querysets.html#django.db.models.query.QuerySet.bulk_create" title="django.db.models.query.QuerySet.bulk_create"><tt class="xref py py-meth docutils literal"><span class="pre">QuerySet.bulk_create()</span></tt></a>. If you need to execute some custom logic when a relationship is created, listen to the <a class="reference internal" href="../signals.html#django.db.models.signals.m2m_changed" title="django.db.models.signals.m2m_changed"><tt class="xref py py-data docutils literal"><span class="pre">m2m_changed</span></tt></a> signal.</p> </dd></dl> <dl class="method"> <dt id="django.db.models.fields.related.RelatedManager.create"> <tt class="descname">create</tt>(<em>**kwargs</em>)<a class="headerlink" href="#django.db.models.fields.related.RelatedManager.create" title="Permalink to this definition">¶</a></dt> <dd><p>Creates a new object, saves it and puts it in the related object set. Returns the newly created object:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">b</span> <span class="o">=</span> <span class="n">Blog</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="nb">id</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">e</span> <span class="o">=</span> <span class="n">b</span><span class="o">.</span><span class="n">entry_set</span><span class="o">.</span><span class="n">create</span><span class="p">(</span> <span class="gp">... </span> <span class="n">headline</span><span class="o">=</span><span class="s">'Hello'</span><span class="p">,</span> <span class="gp">... </span> <span class="n">body_text</span><span class="o">=</span><span class="s">'Hi'</span><span class="p">,</span> <span class="gp">... </span> <span class="n">pub_date</span><span class="o">=</span><span class="n">datetime</span><span class="o">.</span><span class="n">date</span><span class="p">(</span><span class="mi">2005</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span> <span class="gp">... </span><span class="p">)</span> <span class="go"># No need to call e.save() at this point -- it's already been saved.</span> </pre></div> </div> <p>This is equivalent to (but much simpler than):</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">b</span> <span class="o">=</span> <span class="n">Blog</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="nb">id</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">e</span> <span class="o">=</span> <span class="n">Entry</span><span class="p">(</span> <span class="gp">... </span> <span class="n">blog</span><span class="o">=</span><span class="n">b</span><span class="p">,</span> <span class="gp">... </span> <span class="n">headline</span><span class="o">=</span><span class="s">'Hello'</span><span class="p">,</span> <span class="gp">... </span> <span class="n">body_text</span><span class="o">=</span><span class="s">'Hi'</span><span class="p">,</span> <span class="gp">... </span> <span class="n">pub_date</span><span class="o">=</span><span class="n">datetime</span><span class="o">.</span><span class="n">date</span><span class="p">(</span><span class="mi">2005</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span> <span class="gp">... </span><span class="p">)</span> <span class="gp">>>> </span><span class="n">e</span><span class="o">.</span><span class="n">save</span><span class="p">(</span><span class="n">force_insert</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span> </pre></div> </div> <p>Note that there’s no need to specify the keyword argument of the model that defines the relationship. In the above example, we don’t pass the parameter <tt class="docutils literal"><span class="pre">blog</span></tt> to <tt class="docutils literal"><span class="pre">create()</span></tt>. Django figures out that the new <tt class="docutils literal"><span class="pre">Entry</span></tt> object’s <tt class="docutils literal"><span class="pre">blog</span></tt> field should be set to <tt class="docutils literal"><span class="pre">b</span></tt>.</p> </dd></dl> <dl class="method"> <dt id="django.db.models.fields.related.RelatedManager.remove"> <tt class="descname">remove</tt>(<em>obj1</em><span class="optional">[</span>, <em>obj2</em>, <em>...</em><span class="optional">]</span>)<a class="headerlink" href="#django.db.models.fields.related.RelatedManager.remove" title="Permalink to this definition">¶</a></dt> <dd><p>Removes the specified model objects from the related object set:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">b</span> <span class="o">=</span> <span class="n">Blog</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="nb">id</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">e</span> <span class="o">=</span> <span class="n">Entry</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="nb">id</span><span class="o">=</span><span class="mi">234</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">b</span><span class="o">.</span><span class="n">entry_set</span><span class="o">.</span><span class="n">remove</span><span class="p">(</span><span class="n">e</span><span class="p">)</span> <span class="c"># Disassociates Entry e from Blog b.</span> </pre></div> </div> <p>Similar to <a class="reference internal" href="#django.db.models.fields.related.RelatedManager.add" title="django.db.models.fields.related.RelatedManager.add"><tt class="xref py py-meth docutils literal"><span class="pre">add()</span></tt></a>, <tt class="docutils literal"><span class="pre">e.save()</span></tt> is called in the example above to perform the update. Using <tt class="docutils literal"><span class="pre">remove()</span></tt> with a many-to-many relationship, however, will delete the relationships using <a class="reference internal" href="querysets.html#django.db.models.query.QuerySet.delete" title="django.db.models.query.QuerySet.delete"><tt class="xref py py-meth docutils literal"><span class="pre">QuerySet.delete()</span></tt></a> which means no model <tt class="docutils literal"><span class="pre">save()</span></tt> methods are called; listen to the <a class="reference internal" href="../signals.html#django.db.models.signals.m2m_changed" title="django.db.models.signals.m2m_changed"><tt class="xref py py-data docutils literal"><span class="pre">m2m_changed</span></tt></a> signal if you wish to execute custom code when a relationship is deleted.</p> <p>For <a class="reference internal" href="fields.html#django.db.models.ForeignKey" title="django.db.models.ForeignKey"><tt class="xref py py-class docutils literal"><span class="pre">ForeignKey</span></tt></a> objects, this method only exists if <tt class="docutils literal"><span class="pre">null=True</span></tt>. If the related field can’t be set to <tt class="docutils literal"><span class="pre">None</span></tt> (<tt class="docutils literal"><span class="pre">NULL</span></tt>), then an object can’t be removed from a relation without being added to another. In the above example, removing <tt class="docutils literal"><span class="pre">e</span></tt> from <tt class="docutils literal"><span class="pre">b.entry_set()</span></tt> is equivalent to doing <tt class="docutils literal"><span class="pre">e.blog</span> <span class="pre">=</span> <span class="pre">None</span></tt>, and because the <tt class="docutils literal"><span class="pre">blog</span></tt> <a class="reference internal" href="fields.html#django.db.models.ForeignKey" title="django.db.models.ForeignKey"><tt class="xref py py-class docutils literal"><span class="pre">ForeignKey</span></tt></a> doesn’t have <tt class="docutils literal"><span class="pre">null=True</span></tt>, this is invalid.</p> </dd></dl> <dl class="method"> <dt id="django.db.models.fields.related.RelatedManager.clear"> <tt class="descname">clear</tt>()<a class="headerlink" href="#django.db.models.fields.related.RelatedManager.clear" title="Permalink to this definition">¶</a></dt> <dd><p>Removes all objects from the related object set:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">b</span> <span class="o">=</span> <span class="n">Blog</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="nb">id</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">b</span><span class="o">.</span><span class="n">entry_set</span><span class="o">.</span><span class="n">clear</span><span class="p">()</span> </pre></div> </div> <p>Note this doesn’t delete the related objects – it just disassociates them.</p> <p>Just like <tt class="docutils literal"><span class="pre">remove()</span></tt>, <tt class="docutils literal"><span class="pre">clear()</span></tt> is only available on <a class="reference internal" href="fields.html#django.db.models.ForeignKey" title="django.db.models.ForeignKey"><tt class="xref py py-class docutils literal"><span class="pre">ForeignKey</span></tt></a>s where <tt class="docutils literal"><span class="pre">null=True</span></tt>.</p> </dd></dl> </dd></dl> </div> </div> </div> </div> <div class="yui-b" id="sidebar"> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <h3>Browse</h3> <ul> <li>Prev: <a href="fields.html">Model field reference</a></li> <li>Next: <a href="options.html">Model <tt class="docutils literal"><span class="pre">Meta</span></tt> options</a></li> </ul> <h3>You are here:</h3> <ul> <li> <a href="../../index.html">Django 1.5.8 documentation</a> <ul><li><a href="../index.html">API Reference</a> <ul><li><a href="index.html">Models</a> <ul><li>Related objects reference</li></ul> </li></ul></li></ul> </li> </ul> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../../_sources/ref/models/relations.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">May 15, 2014</p> </div> </div> <div id="ft"> <div class="nav"> « <a href="fields.html" title="Model field reference">previous</a> | <a href="../index.html" title="API Reference" accesskey="U">up</a> | <a href="options.html" title="Model <tt class="docutils literal"><span class="pre">Meta</span></tt> options">next</a> »</div> </div> </div> <div class="clearer"></div> </div> </body> </html>