<!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>Many-to-many relationships — Django 1.5.9 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: '1.5.9', 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 1.5.9 documentation" href="../../../index.html" /> <link rel="up" title="Examples of model 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title="Many-to-one relationships">next</a> »</div> </div> <div id="bd"> <div id="yui-main"> <div class="yui-b"> <div class="yui-g" id="topics-db-examples-many_to_many"> <div class="section" id="s-many-to-many-relationships"> <span id="many-to-many-relationships"></span><h1>Many-to-many relationships<a class="headerlink" href="#many-to-many-relationships" title="Permalink to this headline">ΒΆ</a></h1> <p>To define a many-to-many relationship, use <a class="reference internal" href="../../../ref/models/fields.html#ref-manytomany"><em>ManyToManyField</em></a>.</p> <p>In this example, an <tt class="docutils literal"><span class="pre">Article</span></tt> can be published in multiple <tt class="docutils literal"><span class="pre">Publication</span></tt> objects, and a <tt class="docutils literal"><span class="pre">Publication</span></tt> has multiple <tt class="docutils literal"><span class="pre">Article</span></tt> objects:</p> <div class="highlight-python"><div class="highlight"><pre><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">Publication</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">30</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">title</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">'title'</span><span class="p">,)</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">headline</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">publications</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">Publication</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">headline</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">'headline'</span><span class="p">,)</span> </pre></div> </div> <p>What follows are examples of operations that can be performed using the Python API facilities.</p> <p>Create a couple of <tt class="docutils literal"><span class="pre">Publications</span></tt>:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">p1</span> <span class="o">=</span> <span class="n">Publication</span><span class="p">(</span><span class="n">title</span><span class="o">=</span><span class="s">'The Python Journal'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">p1</span><span class="o">.</span><span class="n">save</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">p2</span> <span class="o">=</span> <span class="n">Publication</span><span class="p">(</span><span class="n">title</span><span class="o">=</span><span class="s">'Science News'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">p2</span><span class="o">.</span><span class="n">save</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">p3</span> <span class="o">=</span> <span class="n">Publication</span><span class="p">(</span><span class="n">title</span><span class="o">=</span><span class="s">'Science Weekly'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">p3</span><span class="o">.</span><span class="n">save</span><span class="p">()</span> </pre></div> </div> <p>Create an <tt class="docutils literal"><span class="pre">Article</span></tt>:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">a1</span> <span class="o">=</span> <span class="n">Article</span><span class="p">(</span><span class="n">headline</span><span class="o">=</span><span class="s">'Django lets you build Web apps easily'</span><span class="p">)</span> </pre></div> </div> <p>You can’t associate it with a <tt class="docutils literal"><span class="pre">Publication</span></tt> until it’s been saved:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">a1</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">p1</span><span class="p">)</span> <span class="gt">Traceback (most recent call last):</span> <span class="c">...</span> <span class="gr">ValueError</span>: <span class="n">'Article' instance needs to have a primary key value before a many-to-many relationship can be used.</span> </pre></div> </div> <p>Save it!</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">a1</span><span class="o">.</span><span class="n">save</span><span class="p">()</span> </pre></div> </div> <p>Associate the <tt class="docutils literal"><span class="pre">Article</span></tt> with a <tt class="docutils literal"><span class="pre">Publication</span></tt>:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">a1</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">p1</span><span class="p">)</span> </pre></div> </div> <p>Create another <tt class="docutils literal"><span class="pre">Article</span></tt>, and set it to appear in both <tt class="docutils literal"><span class="pre">Publications</span></tt>:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">a2</span> <span class="o">=</span> <span class="n">Article</span><span class="p">(</span><span class="n">headline</span><span class="o">=</span><span class="s">'NASA uses Python'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">a2</span><span class="o">.</span><span class="n">save</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">a2</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">p1</span><span class="p">,</span> <span class="n">p2</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">a2</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">p3</span><span class="p">)</span> </pre></div> </div> <p>Adding a second time is OK:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">a2</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">p3</span><span class="p">)</span> </pre></div> </div> <p>Adding an object of the wrong type raises <a class="reference external" href="http://docs.python.org/2.7/library/exceptions.html#exceptions.TypeError" title="(in Python v2.7)"><tt class="xref py py-exc docutils literal"><span class="pre">TypeError</span></tt></a>:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">a2</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">a1</span><span class="p">)</span> <span class="gt">Traceback (most recent call last):</span> <span class="c">...</span> <span class="gr">TypeError</span>: <span class="n">'Publication' instance expected</span> </pre></div> </div> <p>Create and add a <tt class="docutils literal"><span class="pre">Publication</span></tt> to an <tt class="docutils literal"><span class="pre">Article</span></tt> in one step using <a class="reference internal" href="../../../ref/models/relations.html#django.db.models.fields.related.RelatedManager.create" title="django.db.models.fields.related.RelatedManager.create"><tt class="xref py py-meth docutils literal"><span class="pre">create()</span></tt></a>:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">new_publication</span> <span class="o">=</span> <span class="n">a2</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">create</span><span class="p">(</span><span class="n">title</span><span class="o">=</span><span class="s">'Highlights for Children'</span><span class="p">)</span> </pre></div> </div> <p><tt class="docutils literal"><span class="pre">Article</span></tt> objects have access to their related <tt class="docutils literal"><span class="pre">Publication</span></tt> objects:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">a1</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Publication: The Python Journal>]</span> <span class="gp">>>> </span><span class="n">a2</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]</span> </pre></div> </div> <p><tt class="docutils literal"><span class="pre">Publication</span></tt> objects have access to their related <tt class="docutils literal"><span class="pre">Article</span></tt> objects:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">p2</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Article: NASA uses Python>]</span> <span class="gp">>>> </span><span class="n">p1</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]</span> <span class="gp">>>> </span><span class="n">Publication</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">4</span><span class="p">)</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Article: NASA uses Python>]</span> </pre></div> </div> <p>Many-to-many relationships can be queried using <a class="reference internal" href="../queries.html#lookups-that-span-relationships"><em>lookups across relationships</em></a>:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">Article</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">publications__id__exact</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span> <span class="go">[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]</span> <span class="gp">>>> </span><span class="n">Article</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">publications__pk</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span> <span class="go">[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]</span> <span class="gp">>>> </span><span class="n">Article</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">publications</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span> <span class="go">[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]</span> <span class="gp">>>> </span><span class="n">Article</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">publications</span><span class="o">=</span><span class="n">p1</span><span class="p">)</span> <span class="go">[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]</span> <span class="gp">>>> </span><span class="n">Article</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">publications__title__startswith</span><span class="o">=</span><span class="s">"Science"</span><span class="p">)</span> <span class="go">[<Article: NASA uses Python>, <Article: NASA uses Python>]</span> <span class="gp">>>> </span><span class="n">Article</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">publications__title__startswith</span><span class="o">=</span><span class="s">"Science"</span><span class="p">)</span><span class="o">.</span><span class="n">distinct</span><span class="p">()</span> <span class="go">[<Article: NASA uses Python>]</span> </pre></div> </div> <p>The <a class="reference internal" href="../../../ref/models/querysets.html#django.db.models.query.QuerySet.count" title="django.db.models.query.QuerySet.count"><tt class="xref py py-meth docutils literal"><span class="pre">count()</span></tt></a> function respects <a class="reference internal" href="../../../ref/models/querysets.html#django.db.models.query.QuerySet.distinct" title="django.db.models.query.QuerySet.distinct"><tt class="xref py py-meth docutils literal"><span class="pre">distinct()</span></tt></a> as well:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">Article</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">publications__title__startswith</span><span class="o">=</span><span class="s">"Science"</span><span class="p">)</span><span class="o">.</span><span class="n">count</span><span class="p">()</span> <span class="go">2</span> <span class="gp">>>> </span><span class="n">Article</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">publications__title__startswith</span><span class="o">=</span><span class="s">"Science"</span><span class="p">)</span><span class="o">.</span><span class="n">distinct</span><span class="p">()</span><span class="o">.</span><span class="n">count</span><span class="p">()</span> <span class="go">1</span> <span class="gp">>>> </span><span class="n">Article</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">publications__in</span><span class="o">=</span><span class="p">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">])</span><span class="o">.</span><span class="n">distinct</span><span class="p">()</span> <span class="go">[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]</span> <span class="gp">>>> </span><span class="n">Article</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">publications__in</span><span class="o">=</span><span class="p">[</span><span class="n">p1</span><span class="p">,</span><span class="n">p2</span><span class="p">])</span><span class="o">.</span><span class="n">distinct</span><span class="p">()</span> <span class="go">[<Article: Django lets you build Web apps easily>, <Article: NASA uses Python>]</span> </pre></div> </div> <p>Reverse m2m queries are supported (i.e., starting at the table that doesn’t have a <a class="reference internal" href="../../../ref/models/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>):</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">Publication</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">id__exact</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span> <span class="go">[<Publication: The Python Journal>]</span> <span class="gp">>>> </span><span class="n">Publication</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">pk</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span> <span class="go">[<Publication: The Python Journal>]</span> <span class="gp">>>> </span><span class="n">Publication</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">article__headline__startswith</span><span class="o">=</span><span class="s">"NASA"</span><span class="p">)</span> <span class="go">[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]</span> <span class="gp">>>> </span><span class="n">Publication</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">article__id__exact</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span> <span class="go">[<Publication: The Python Journal>]</span> <span class="gp">>>> </span><span class="n">Publication</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">article__pk</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span> <span class="go">[<Publication: The Python Journal>]</span> <span class="gp">>>> </span><span class="n">Publication</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">article</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span> <span class="go">[<Publication: The Python Journal>]</span> <span class="gp">>>> </span><span class="n">Publication</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">article</span><span class="o">=</span><span class="n">a1</span><span class="p">)</span> <span class="go">[<Publication: The Python Journal>]</span> <span class="gp">>>> </span><span class="n">Publication</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">article__in</span><span class="o">=</span><span class="p">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">])</span><span class="o">.</span><span class="n">distinct</span><span class="p">()</span> <span class="go">[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]</span> <span class="gp">>>> </span><span class="n">Publication</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">article__in</span><span class="o">=</span><span class="p">[</span><span class="n">a1</span><span class="p">,</span><span class="n">a2</span><span class="p">])</span><span class="o">.</span><span class="n">distinct</span><span class="p">()</span> <span class="go">[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]</span> </pre></div> </div> <p>Excluding a related item works as you would expect, too (although the SQL involved is a little complex):</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">Article</span><span class="o">.</span><span class="n">objects</span><span class="o">.</span><span class="n">exclude</span><span class="p">(</span><span class="n">publications</span><span class="o">=</span><span class="n">p2</span><span class="p">)</span> <span class="go">[<Article: Django lets you build Web apps easily>]</span> </pre></div> </div> <p>If we delete a <tt class="docutils literal"><span class="pre">Publication</span></tt>, its <tt class="docutils literal"><span class="pre">Articles</span></tt> won’t be able to access it:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">p1</span><span class="o">.</span><span class="n">delete</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">Publication</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="go">[<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>]</span> <span class="gp">>>> </span><span class="n">a1</span> <span class="o">=</span> <span class="n">Article</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">pk</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">a1</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[]</span> </pre></div> </div> <p>If we delete an <tt class="docutils literal"><span class="pre">Article</span></tt>, its <tt class="docutils literal"><span class="pre">Publications</span></tt> won’t be able to access it:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">a2</span><span class="o">.</span><span class="n">delete</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">Article</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="go">[<Article: Django lets you build Web apps easily>]</span> <span class="gp">>>> </span><span class="n">p2</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[]</span> </pre></div> </div> <p>Adding via the ‘other’ end of an m2m:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">a4</span> <span class="o">=</span> <span class="n">Article</span><span class="p">(</span><span class="n">headline</span><span class="o">=</span><span class="s">'NASA finds intelligent life on Earth'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">a4</span><span class="o">.</span><span class="n">save</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">p2</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">a4</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">p2</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Article: NASA finds intelligent life on Earth>]</span> <span class="gp">>>> </span><span class="n">a4</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Publication: Science News>]</span> </pre></div> </div> <p>Adding via the other end using keywords:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">new_article</span> <span class="o">=</span> <span class="n">p2</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">create</span><span class="p">(</span><span class="n">headline</span><span class="o">=</span><span class="s">'Oxygen-free diet works wonders'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">p2</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Article: NASA finds intelligent life on Earth>, <Article: Oxygen-free diet works wonders>]</span> <span class="gp">>>> </span><span class="n">a5</span> <span class="o">=</span> <span class="n">p2</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">all</span><span class="p">()[</span><span class="mi">1</span><span class="p">]</span> <span class="gp">>>> </span><span class="n">a5</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Publication: Science News>]</span> </pre></div> </div> <p>Removing <tt class="docutils literal"><span class="pre">Publication</span></tt> from an <tt class="docutils literal"><span class="pre">Article</span></tt>:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">a4</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">remove</span><span class="p">(</span><span class="n">p2</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">p2</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Article: Oxygen-free diet works wonders>]</span> <span class="gp">>>> </span><span class="n">a4</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[]</span> </pre></div> </div> <p>And from the other end:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">p2</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">remove</span><span class="p">(</span><span class="n">a5</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">p2</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[]</span> <span class="gp">>>> </span><span class="n">a5</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[]</span> </pre></div> </div> <p>Relation sets can be assigned. Assignment clears any existing set members:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">a4</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Publication: Science News>]</span> <span class="gp">>>> </span><span class="n">a4</span><span class="o">.</span><span class="n">publications</span> <span class="o">=</span> <span class="p">[</span><span class="n">p3</span><span class="p">]</span> <span class="gp">>>> </span><span class="n">a4</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Publication: Science Weekly>]</span> </pre></div> </div> <p>Relation sets can be cleared:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">p2</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">clear</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">p2</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[]</span> </pre></div> </div> <p>And you can clear from the other end:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">p2</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">a4</span><span class="p">,</span> <span class="n">a5</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">p2</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Article: NASA finds intelligent life on Earth>, <Article: Oxygen-free diet works wonders>]</span> <span class="gp">>>> </span><span class="n">a4</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Publication: Science News>, <Publication: Science Weekly>]</span> <span class="gp">>>> </span><span class="n">a4</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">clear</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">a4</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[]</span> <span class="gp">>>> </span><span class="n">p2</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Article: Oxygen-free diet works wonders>]</span> </pre></div> </div> <p>Recreate the <tt class="docutils literal"><span class="pre">Article</span></tt> and <tt class="docutils literal"><span class="pre">Publication</span></tt> we have deleted:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">p1</span> <span class="o">=</span> <span class="n">Publication</span><span class="p">(</span><span class="n">title</span><span class="o">=</span><span class="s">'The Python Journal'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">p1</span><span class="o">.</span><span class="n">save</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">a2</span> <span class="o">=</span> <span class="n">Article</span><span class="p">(</span><span class="n">headline</span><span class="o">=</span><span class="s">'NASA uses Python'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">a2</span><span class="o">.</span><span class="n">save</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">a2</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">p1</span><span class="p">,</span> <span class="n">p2</span><span class="p">,</span> <span class="n">p3</span><span class="p">)</span> </pre></div> </div> <p>Bulk delete some <tt class="docutils literal"><span class="pre">Publications</span></tt> - references to deleted publications should go:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">Publication</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">title__startswith</span><span class="o">=</span><span class="s">'Science'</span><span class="p">)</span><span class="o">.</span><span class="n">delete</span><span class="p">()</span> <span class="gp">>>> </span><span class="n">Publication</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="go">[<Publication: Highlights for Children>, <Publication: The Python Journal>]</span> <span class="gp">>>> </span><span class="n">Article</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="go">[<Article: Django lets you build Web apps easily>, <Article: NASA finds intelligent life on Earth>, <Article: NASA uses Python>, <Article: Oxygen-free diet works wonders>]</span> <span class="gp">>>> </span><span class="n">a2</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Publication: The Python Journal>]</span> </pre></div> </div> <p>Bulk delete some articles - references to deleted objects should go:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">q</span> <span class="o">=</span> <span class="n">Article</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">headline__startswith</span><span class="o">=</span><span class="s">'Django'</span><span class="p">)</span> <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">q</span><span class="p">)</span> <span class="go">[<Article: Django lets you build Web apps easily>]</span> <span class="gp">>>> </span><span class="n">q</span><span class="o">.</span><span class="n">delete</span><span class="p">()</span> </pre></div> </div> <p>After the <a class="reference internal" href="../../../ref/models/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">delete()</span></tt></a>, the <a class="reference internal" href="../../../ref/models/querysets.html#django.db.models.query.QuerySet" title="django.db.models.query.QuerySet"><tt class="xref py py-class docutils literal"><span class="pre">QuerySet</span></tt></a> cache needs to be cleared, and the referenced objects should be gone:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">q</span><span class="p">)</span> <span class="go">[]</span> <span class="gp">>>> </span><span class="n">p1</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Article: NASA uses Python>]</span> </pre></div> </div> <p>An alternate to calling <a class="reference internal" href="../../../ref/models/relations.html#django.db.models.fields.related.RelatedManager.clear" title="django.db.models.fields.related.RelatedManager.clear"><tt class="xref py py-meth docutils literal"><span class="pre">clear()</span></tt></a> is to assign the empty set:</p> <div class="highlight-pycon"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">p1</span><span class="o">.</span><span class="n">article_set</span> <span class="o">=</span> <span class="p">[]</span> <span class="gp">>>> </span><span class="n">p1</span><span class="o">.</span><span class="n">article_set</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[]</span> <span class="gp">>>> </span><span class="n">a2</span><span class="o">.</span><span class="n">publications</span> <span class="o">=</span> <span class="p">[</span><span class="n">p1</span><span class="p">,</span> <span class="n">new_publication</span><span class="p">]</span> <span class="gp">>>> </span><span class="n">a2</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[<Publication: Highlights for Children>, <Publication: The Python Journal>]</span> <span class="gp">>>> </span><span class="n">a2</span><span class="o">.</span><span class="n">publications</span> <span class="o">=</span> <span class="p">[]</span> <span class="gp">>>> </span><span class="n">a2</span><span class="o">.</span><span class="n">publications</span><span class="o">.</span><span class="n">all</span><span class="p">()</span> <span class="go">[]</span> </pre></div> </div> </div> </div> </div> </div> <div class="yui-b" id="sidebar"> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <h3>Browse</h3> <ul> <li>Prev: <a href="index.html">Examples of model relationship API usage</a></li> <li>Next: <a href="many_to_one.html">Many-to-one relationships</a></li> </ul> <h3>You are here:</h3> <ul> <li> <a href="../../../index.html">Django 1.5.9 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