<!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" lang="">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Related objects reference — Django 1.8.19 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: '1.8.19',
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="index" title="Index" href="../../genindex.html" />
<link rel="search" title="Search" href="../../search.html" />
<link rel="top" title="Django 1.8.19 documentation" href="../../contents.html" />
<link rel="up" title="Models" href="index.html" />
<link rel="next" title="Model class reference" href="class.html" />
<link rel="prev" title="Model _meta API" href="meta.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 role="document">
<div class="document">
<div id="custom-doc" class="yui-t6">
<div id="hd">
<h1><a href="../../index.html">Django 1.8.19 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="meta.html" title="Model <code class="docutils literal"><span class="pre">_meta</span></code> API">previous</a>
|
<a href="../index.html" title="API Reference" accesskey="U">up</a>
|
<a href="class.html" title="Model class reference">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><code class="descname">RelatedManager</code><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"><code class="xref py py-class docutils literal"><span class="pre">ForeignKey</span></code></a> relation.
That is:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">django.db</span> <span class="k">import</span> <span class="n">models</span>
<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="c1"># ...</span>
<span class="k">pass</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 <code class="docutils literal"><span class="pre">reporter.article_set</span></code>.</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"><code class="xref py py-class docutils literal"><span class="pre">ManyToManyField</span></code></a> relation:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><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="c1"># ...</span>
<span class="k">pass</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
<code class="docutils literal"><span class="pre">topping.pizza_set</span></code> and on <code class="docutils literal"><span class="pre">pizza.toppings</span></code>.</p>
</li>
</ul>
<dl class="method">
<dt id="django.db.models.fields.related.RelatedManager.add">
<code class="descname">add</code>(<em>*objs</em>)<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-default"><div class="highlight"><pre><span></span><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="c1"># Associates Entry e with Blog b.</span>
</pre></div>
</div>
<p>In the example above, in the case of a
<a class="reference internal" href="fields.html#django.db.models.ForeignKey" title="django.db.models.ForeignKey"><code class="xref py py-class docutils literal"><span class="pre">ForeignKey</span></code></a> relationship,
<code class="docutils literal"><span class="pre">e.save()</span></code> is called by the related manager to perform the update.
Using <code class="docutils literal"><span class="pre">add()</span></code> with a many-to-many relationship, however, will not
call any <code class="docutils literal"><span class="pre">save()</span></code> 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"><code class="xref py py-meth docutils literal"><span class="pre">QuerySet.bulk_create()</span></code></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"><code class="xref py py-data docutils literal"><span class="pre">m2m_changed</span></code></a> signal.</p>
</dd></dl>
<dl class="method">
<dt id="django.db.models.fields.related.RelatedManager.create">
<code class="descname">create</code>(<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-default"><div class="highlight"><pre><span></span><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="s1">'Hello'</span><span class="p">,</span>
<span class="gp">... </span> <span class="n">body_text</span><span class="o">=</span><span class="s1">'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-default"><div class="highlight"><pre><span></span><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="s1">'Hello'</span><span class="p">,</span>
<span class="gp">... </span> <span class="n">body_text</span><span class="o">=</span><span class="s1">'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="kc">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 <code class="docutils literal"><span class="pre">blog</span></code> to <code class="docutils literal"><span class="pre">create()</span></code>. Django figures out that the new
<code class="docutils literal"><span class="pre">Entry</span></code> object’s <code class="docutils literal"><span class="pre">blog</span></code> field should be set to <code class="docutils literal"><span class="pre">b</span></code>.</p>
</dd></dl>
<dl class="method">
<dt id="django.db.models.fields.related.RelatedManager.remove">
<code class="descname">remove</code>(<em>*objs</em>)<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-default"><div class="highlight"><pre><span></span><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="c1"># 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"><code class="xref py py-meth docutils literal"><span class="pre">add()</span></code></a>, <code class="docutils literal"><span class="pre">e.save()</span></code> is called in the example above
to perform the update. Using <code class="docutils literal"><span class="pre">remove()</span></code> 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"><code class="xref py py-meth docutils literal"><span class="pre">QuerySet.delete()</span></code></a> which
means no model <code class="docutils literal"><span class="pre">save()</span></code> 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"><code class="xref py py-data docutils literal"><span class="pre">m2m_changed</span></code></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"><code class="xref py py-class docutils literal"><span class="pre">ForeignKey</span></code></a> objects, this method only
exists if <code class="docutils literal"><span class="pre">null=True</span></code>. If the related field can’t be set to <code class="docutils literal"><span class="pre">None</span></code>
(<code class="docutils literal"><span class="pre">NULL</span></code>), then an object can’t be removed from a relation without
being added to another. In the above example, removing <code class="docutils literal"><span class="pre">e</span></code> from
<code class="docutils literal"><span class="pre">b.entry_set()</span></code> is equivalent to doing <code class="docutils literal"><span class="pre">e.blog</span> <span class="pre">=</span> <span class="pre">None</span></code>, and because
the <code class="docutils literal"><span class="pre">blog</span></code> <a class="reference internal" href="fields.html#django.db.models.ForeignKey" title="django.db.models.ForeignKey"><code class="xref py py-class docutils literal"><span class="pre">ForeignKey</span></code></a> doesn’t have
<code class="docutils literal"><span class="pre">null=True</span></code>, this is invalid.</p>
<div class="versionchanged">
<span class="title">Changed in Django 1.7.</span> </div>
<p>For <a class="reference internal" href="fields.html#django.db.models.ForeignKey" title="django.db.models.ForeignKey"><code class="xref py py-class docutils literal"><span class="pre">ForeignKey</span></code></a> objects, this method accepts
a <code class="docutils literal"><span class="pre">bulk</span></code> argument to control how to perform the operation.
If <code class="docutils literal"><span class="pre">True</span></code> (the default), <code class="docutils literal"><span class="pre">QuerySet.update()</span></code> is used.
If <code class="docutils literal"><span class="pre">bulk=False</span></code>, the <code class="docutils literal"><span class="pre">save()</span></code> method of each individual model
instance is called instead. This triggers the
<a class="reference internal" href="../signals.html#django.db.models.signals.pre_save" title="django.db.models.signals.pre_save"><code class="xref py py-data docutils literal"><span class="pre">pre_save</span></code></a> and
<a class="reference internal" href="../signals.html#django.db.models.signals.post_save" title="django.db.models.signals.post_save"><code class="xref py py-data docutils literal"><span class="pre">post_save</span></code></a> signals and comes at the
expense of performance.</p>
</dd></dl>
<dl class="method">
<dt id="django.db.models.fields.related.RelatedManager.clear">
<code class="descname">clear</code>()<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-default"><div class="highlight"><pre><span></span><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 <code class="docutils literal"><span class="pre">remove()</span></code>, <code class="docutils literal"><span class="pre">clear()</span></code> is only available on
<a class="reference internal" href="fields.html#django.db.models.ForeignKey" title="django.db.models.ForeignKey"><code class="xref py py-class docutils literal"><span class="pre">ForeignKey</span></code></a>s where <code class="docutils literal"><span class="pre">null=True</span></code> and it also
accepts the <code class="docutils literal"><span class="pre">bulk</span></code> keyword argument.</p>
</dd></dl>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p>Note that <code class="docutils literal"><span class="pre">add()</span></code>, <code class="docutils literal"><span class="pre">create()</span></code>, <code class="docutils literal"><span class="pre">remove()</span></code>, and <code class="docutils literal"><span class="pre">clear()</span></code> all
apply database changes immediately for all types of related fields. In
other words, there is no need to call <code class="docutils literal"><span class="pre">save()</span></code> on either end of the
relationship.</p>
<p class="last">Also, if you are using <a class="reference internal" href="../../topics/db/models.html#intermediary-manytomany"><span class="std std-ref">an intermediate model</span></a> for a many-to-many relationship, some of the
related manager’s methods are disabled.</p>
</div>
</dd></dl>
<div class="section" id="s-direct-assignment">
<span id="s-id1"></span><span id="direct-assignment"></span><span id="id1"></span><h2>Direct Assignment<a class="headerlink" href="#direct-assignment" title="Permalink to this headline">¶</a></h2>
<p>A related object set can be replaced in bulk with one operation by assigning a
new iterable of objects to it:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">new_list</span> <span class="o">=</span> <span class="p">[</span><span class="n">obj1</span><span class="p">,</span> <span class="n">obj2</span><span class="p">,</span> <span class="n">obj3</span><span class="p">]</span>
<span class="gp">>>> </span><span class="n">e</span><span class="o">.</span><span class="n">related_set</span> <span class="o">=</span> <span class="n">new_list</span>
</pre></div>
</div>
<p>If the foreign key relationship has <code class="docutils literal"><span class="pre">null=True</span></code>, then the related manager
will first call <code class="docutils literal"><span class="pre">clear()</span></code> to disassociate any existing objects in the related
set before adding the contents of <code class="docutils literal"><span class="pre">new_list</span></code>. Otherwise the objects in
<code class="docutils literal"><span class="pre">new_list</span></code> will be added to the existing related object set.</p>
</div>
</div>
</div>
</div>
</div>
<div class="yui-b" id="sidebar">
<div class="sphinxsidebar" role="navigation" aria-label="main navigation">
<div class="sphinxsidebarwrapper">
<h3><a href="../../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Related objects reference</a><ul>
<li><a class="reference internal" href="#direct-assignment">Direct Assignment</a></li>
</ul>
</li>
</ul>
<h3>Browse</h3>
<ul>
<li>Prev: <a href="meta.html">Model <code class="docutils literal"><span class="pre">_meta</span></code> API</a></li>
<li>Next: <a href="class.html">Model class reference</a></li>
</ul>
<h3>You are here:</h3>
<ul>
<li>
<a href="../../index.html">Django 1.8.19 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>
<div role="note" aria-label="source link">
<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>
<div id="searchbox" style="display: none" role="search">
<h3>Quick search</h3>
<form class="search" action="../../search.html" method="get">
<div><input type="text" name="q" /></div>
<div><input type="submit" value="Go" /></div>
<input type="hidden" name="check_keywords" value="yes" />
<input type="hidden" name="area" value="default" />
</form>
</div>
<script type="text/javascript">$('#searchbox').show(0);</script>
</div>
</div>
<h3>Last update:</h3>
<p class="topless">Mar 10, 2018</p>
</div>
</div>
<div id="ft">
<div class="nav">
« <a href="meta.html" title="Model <code class="docutils literal"><span class="pre">_meta</span></code> API">previous</a>
|
<a href="../index.html" title="API Reference" accesskey="U">up</a>
|
<a href="class.html" title="Model class reference">next</a> »</div>
</div>
</div>
<div class="clearer"></div>
</div>
</body>
</html>
