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<div class="section" id="bi-directional-references">
<h1>Bi-Directional References<a class="headerlink" href="#bi-directional-references" title="Permalink to this headline"></a></h1>
<p>By default when you map a bi-directional reference, the reference is maintained on both sides
of the relationship and there is not a single &quot;owning side&quot;. Both sides are considered owning
and changes are tracked and persisted separately. Here is an example:</p>
<div class="highlight-php"><div class="highlight"><pre><span class="cp">&lt;?php</span>
<span class="sd">/** @Document */</span>
<span class="k">class</span> <span class="nc">BlogPost</span>
<span class="p">{</span>
<span class="c1">// ...</span>
<span class="sd">/** @ReferenceOne(targetDocument=&quot;User&quot;) */</span>
<span class="k">private</span> <span class="nv">$user</span><span class="p">;</span>
<span class="p">}</span>
<span class="sd">/** @Document */</span>
<span class="k">class</span> <span class="nc">User</span>
<span class="p">{</span>
<span class="c1">// ...</span>
<span class="sd">/** @ReferenceMany(targetDocument=&quot;BlogPost&quot;) */</span>
<span class="k">private</span> <span class="nv">$posts</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
<p>When I persist some instances of the above classes the references would exist on both sides! The
<code class="docutils literal"><span class="pre">BlogPost</span></code> collection would have a <a class="reference external" href="https://docs.mongodb.com/manual/reference/database-references/#dbrefs">DBRef</a> stored on the <code class="docutils literal"><span class="pre">$user</span></code> property and the <code class="docutils literal"><span class="pre">User</span></code>
collection would have a <a class="reference external" href="https://docs.mongodb.com/manual/reference/database-references/#dbrefs">DBRef</a> stored in the <code class="docutils literal"><span class="pre">$posts</span></code> property.</p>
<div class="section" id="owning-and-inverse-sides">
<h2>Owning and Inverse Sides<a class="headerlink" href="#owning-and-inverse-sides" title="Permalink to this headline"></a></h2>
<p>A user may have lots of posts and we don't need to store a reference to each post on the user, we
can get the users post by running a query like the following:</p>
<div class="highlight-javascript"><div class="highlight"><pre><span class="nx">db</span><span class="p">.</span><span class="nx">BlogPost</span><span class="p">.</span><span class="nx">find</span><span class="p">({</span> <span class="s1">&#39;user.$id&#39;</span> <span class="o">:</span> <span class="nx">user</span><span class="p">.</span><span class="nx">id</span> <span class="p">})</span>
</pre></div>
</div>
<p>In order to map this you can use the <code class="docutils literal"><span class="pre">inversedBy</span></code> and <code class="docutils literal"><span class="pre">mappedBy</span></code> options. Here is the same
example above where we implement this:</p>
<div class="section" id="one-to-many">
<h3>One to Many<a class="headerlink" href="#one-to-many" title="Permalink to this headline"></a></h3>
<div class="highlight-php"><div class="highlight"><pre><span class="cp">&lt;?php</span>
<span class="sd">/** @Document */</span>
<span class="k">class</span> <span class="nc">BlogPost</span>
<span class="p">{</span>
<span class="c1">// ...</span>
<span class="sd">/** @ReferenceOne(targetDocument=&quot;User&quot;, inversedBy=&quot;posts&quot;) */</span>
<span class="k">private</span> <span class="nv">$user</span><span class="p">;</span>
<span class="p">}</span>
<span class="sd">/** @Document */</span>
<span class="k">class</span> <span class="nc">User</span>
<span class="p">{</span>
<span class="c1">// ...</span>
<span class="sd">/** @ReferenceMany(targetDocument=&quot;BlogPost&quot;, mappedBy=&quot;user&quot;) */</span>
<span class="k">private</span> <span class="nv">$posts</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
<p>So now when we persist a <code class="docutils literal"><span class="pre">User</span></code> and multiple <code class="docutils literal"><span class="pre">BlogPost</span></code> instances for that <code class="docutils literal"><span class="pre">User</span></code>:</p>
<div class="highlight-php"><div class="highlight"><pre><span class="cp">&lt;?php</span>
<span class="nv">$user</span> <span class="o">=</span> <span class="k">new</span> <span class="nx">User</span><span class="p">();</span>
<span class="nv">$post1</span> <span class="o">=</span> <span class="k">new</span> <span class="nx">BlogPost</span><span class="p">();</span>
<span class="nv">$post1</span><span class="o">-&gt;</span><span class="na">setUser</span><span class="p">(</span><span class="nv">$user</span><span class="p">);</span>
<span class="nv">$post2</span> <span class="o">=</span> <span class="k">new</span> <span class="nx">BlogPost</span><span class="p">();</span>
<span class="nv">$post2</span><span class="o">-&gt;</span><span class="na">setUser</span><span class="p">(</span><span class="nv">$user</span><span class="p">);</span>
<span class="nv">$post3</span> <span class="o">=</span> <span class="k">new</span> <span class="nx">BlogPost</span><span class="p">();</span>
<span class="nv">$post3</span><span class="o">-&gt;</span><span class="na">setUser</span><span class="p">(</span><span class="nv">$user</span><span class="p">);</span>
<span class="nv">$dm</span><span class="o">-&gt;</span><span class="na">persist</span><span class="p">(</span><span class="nv">$post1</span><span class="p">);</span>
<span class="nv">$dm</span><span class="o">-&gt;</span><span class="na">persist</span><span class="p">(</span><span class="nv">$post2</span><span class="p">);</span>
<span class="nv">$dm</span><span class="o">-&gt;</span><span class="na">persist</span><span class="p">(</span><span class="nv">$post3</span><span class="p">);</span>
<span class="nv">$dm</span><span class="o">-&gt;</span><span class="na">flush</span><span class="p">();</span>
</pre></div>
</div>
<p>And we retrieve the <code class="docutils literal"><span class="pre">User</span></code> later to access the posts for that user:</p>
<div class="highlight-php"><div class="highlight"><pre><span class="cp">&lt;?php</span>
<span class="nv">$user</span> <span class="o">=</span> <span class="nv">$dm</span><span class="o">-&gt;</span><span class="na">find</span><span class="p">(</span><span class="s1">&#39;User&#39;</span><span class="p">,</span> <span class="nv">$user</span><span class="o">-&gt;</span><span class="na">id</span><span class="p">);</span>
<span class="nv">$posts</span> <span class="o">=</span> <span class="nv">$user</span><span class="o">-&gt;</span><span class="na">getPosts</span><span class="p">();</span>
<span class="k">foreach</span> <span class="p">(</span><span class="nv">$posts</span> <span class="k">as</span> <span class="nv">$post</span><span class="p">)</span> <span class="p">{</span>
<span class="c1">// ...</span>
<span class="p">}</span>
</pre></div>
</div>
<p>The above will execute a query like the following to lazily load the collection of posts to
iterate over:</p>
<div class="highlight-javascript"><div class="highlight"><pre><span class="nx">db</span><span class="p">.</span><span class="nx">BlogPost</span><span class="p">.</span><span class="nx">find</span><span class="p">(</span> <span class="p">{</span> <span class="s1">&#39;user.$id&#39;</span> <span class="o">:</span> <span class="nx">user</span><span class="p">.</span><span class="nx">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">Remember that the inverse side, the side which specified <code class="docutils literal"><span class="pre">mappedBy</span></code> is immutable and
any changes to the state of the reference will not be persisted.</p>
</div>
</div>
</div>
<div class="section" id="other-examples">
<h2>Other Examples<a class="headerlink" href="#other-examples" title="Permalink to this headline"></a></h2>
<p>Here are several examples which implement the <code class="docutils literal"><span class="pre">inversedBy</span></code> and <code class="docutils literal"><span class="pre">mappedBy</span></code> options:</p>
<div class="section" id="one-to-one">
<h3>One to One<a class="headerlink" href="#one-to-one" title="Permalink to this headline"></a></h3>
<p>Here is an example where we have a one to one relationship between <code class="docutils literal"><span class="pre">Cart</span></code> and <code class="docutils literal"><span class="pre">Customer</span></code>:</p>
<div class="highlight-php"><div class="highlight"><pre><span class="cp">&lt;?php</span>
<span class="sd">/** @Document */</span>
<span class="k">class</span> <span class="nc">Cart</span>
<span class="p">{</span>
<span class="c1">// ...</span>
<span class="sd">/**</span>
<span class="sd"> * @ReferenceOne(targetDocument=&quot;Customer&quot;, inversedBy=&quot;cart&quot;)</span>
<span class="sd"> */</span>
<span class="k">public</span> <span class="nv">$customer</span><span class="p">;</span>
<span class="p">}</span>
<span class="sd">/** @Document */</span>
<span class="k">class</span> <span class="nc">Customer</span>
<span class="p">{</span>
<span class="c1">// ...</span>
<span class="sd">/**</span>
<span class="sd"> * @ReferenceOne(targetDocument=&quot;Cart&quot;, mappedBy=&quot;customer&quot;)</span>
<span class="sd"> */</span>
<span class="k">public</span> <span class="nv">$cart</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
<p>The owning side is on <code class="docutils literal"><span class="pre">Cart.customer</span></code> and the <code class="docutils literal"><span class="pre">Customer.cart</span></code> referenced is loaded with a query
like this:</p>
<div class="highlight-javascript"><div class="highlight"><pre><span class="nx">db</span><span class="p">.</span><span class="nx">Cart</span><span class="p">.</span><span class="nx">find</span><span class="p">(</span> <span class="p">{</span> <span class="s1">&#39;customer.$id&#39;</span> <span class="o">:</span> <span class="nx">customer</span><span class="p">.</span><span class="nx">id</span> <span class="p">}</span> <span class="p">)</span>
</pre></div>
</div>
<p>If you want to nullify the relationship between a <code class="docutils literal"><span class="pre">Cart</span></code> instance and <code class="docutils literal"><span class="pre">Customer</span></code> instance
you must null it out on the <code class="docutils literal"><span class="pre">Cart.customer</span></code> side:</p>
<div class="highlight-php"><div class="highlight"><pre><span class="cp">&lt;?php</span>
<span class="nv">$cart</span><span class="o">-&gt;</span><span class="na">setCustomer</span><span class="p">(</span><span class="k">null</span><span class="p">);</span>
<span class="nv">$dm</span><span class="o">-&gt;</span><span class="na">flush</span><span class="p">();</span>
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">When specifying inverse one-to-one relationships the referenced document is
loaded directly when the owning document is hydrated instead of using a
proxy. In the example above, loading a <code class="docutils literal"><span class="pre">Customer</span></code> object from the database
would also cause the corresponding <code class="docutils literal"><span class="pre">Cart</span></code> to be loaded. This can cause
performance issues when loading many <code class="docutils literal"><span class="pre">Customer</span></code> objects at once.</p>
</div>
</div>
<div class="section" id="self-referencing-many-to-many">
<h3>Self-Referencing Many to Many<a class="headerlink" href="#self-referencing-many-to-many" title="Permalink to this headline"></a></h3>
<div class="highlight-php"><div class="highlight"><pre><span class="cp">&lt;?php</span>
<span class="k">namespace</span> <span class="nx">Documents</span><span class="p">;</span>
<span class="sd">/** @Document */</span>
<span class="k">class</span> <span class="nc">User</span>
<span class="p">{</span>
<span class="c1">// ...</span>
<span class="sd">/**</span>
<span class="sd"> * @ReferenceMany(targetDocument=&quot;User&quot;, mappedBy=&quot;myFriends&quot;)</span>
<span class="sd"> */</span>
<span class="k">public</span> <span class="nv">$friendsWithMe</span><span class="p">;</span>
<span class="sd">/**</span>
<span class="sd"> * @ReferenceMany(targetDocument=&quot;User&quot;, inversedBy=&quot;friendsWithMe&quot;)</span>
<span class="sd"> */</span>
<span class="k">public</span> <span class="nv">$myFriends</span><span class="p">;</span>
<span class="k">public</span> <span class="k">function</span> <span class="nf">__construct</span><span class="p">(</span><span class="nv">$name</span><span class="p">)</span>
<span class="p">{</span>
<span class="nv">$this</span><span class="o">-&gt;</span><span class="na">name</span> <span class="o">=</span> <span class="nv">$name</span><span class="p">;</span>
<span class="nv">$this</span><span class="o">-&gt;</span><span class="na">friendsWithMe</span> <span class="o">=</span> <span class="k">new</span> <span class="nx">\Doctrine\Common\Collections\ArrayCollection</span><span class="p">();</span>
<span class="nv">$this</span><span class="o">-&gt;</span><span class="na">myFriends</span> <span class="o">=</span> <span class="k">new</span> <span class="nx">\Doctrine\Common\Collections\ArrayCollection</span><span class="p">();</span>
<span class="p">}</span>
<span class="k">public</span> <span class="k">function</span> <span class="nf">addFriend</span><span class="p">(</span><span class="nx">User</span> <span class="nv">$user</span><span class="p">)</span>
<span class="p">{</span>
<span class="nv">$user</span><span class="o">-&gt;</span><span class="na">friendsWithMe</span><span class="p">[]</span> <span class="o">=</span> <span class="nv">$this</span><span class="p">;</span>
<span class="nv">$this</span><span class="o">-&gt;</span><span class="na">myFriends</span><span class="p">[]</span> <span class="o">=</span> <span class="nv">$user</span><span class="p">;</span>
<span class="p">}</span>
<span class="p">}</span>
</pre></div>
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<h3><a href="../index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Bi-Directional References</a><ul>
<li><a class="reference internal" href="#owning-and-inverse-sides">Owning and Inverse Sides</a><ul>
<li><a class="reference internal" href="#one-to-many">One to Many</a></li>
</ul>
</li>
<li><a class="reference internal" href="#other-examples">Other Examples</a><ul>
<li><a class="reference internal" href="#one-to-one">One to One</a></li>
<li><a class="reference internal" href="#self-referencing-many-to-many">Self-Referencing Many to Many</a></li>
</ul>
</li>
</ul>
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<h3>This Page</h3>
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