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<div class="section" id="map-reduce">
<h1>Map Reduce<a class="headerlink" href="#map-reduce" title="Permalink to this headline"></a></h1>
<p>The Doctrine MongoDB ODM fully supports the <a class="reference external" href="https://docs.mongodb.com/manual/core/map-reduce/">map reduce</a> functionality via its
<a class="reference internal" href="query-builder-api.html"><span class="doc">Query Builder API</span></a>.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p>From the MongoDB manual:</p>
<p class="last">Map-reduce is a data processing paradigm for condensing large volumes of
data into useful aggregated results. In MongoDB, map-reduce operations use
custom JavaScript functions to map, or associate, values to a key. If a key
has multiple values mapped to it, the operation reduces the values for the
key to a single object.</p>
</div>
<p>Imagine a situation where you had an application with a document
named <code class="docutils literal"><span class="pre">Event</span></code> and it was related to a <code class="docutils literal"><span class="pre">User</span></code> document:</p>
<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">Event</span>
<span class="p">{</span>
<span class="sd">/** @Id */</span>
<span class="k">private</span> <span class="nv">$id</span><span class="p">;</span>
<span class="sd">/** @ReferenceOne(targetDocument=&quot;Documents\User&quot;) */</span>
<span class="k">private</span> <span class="nv">$user</span><span class="p">;</span>
<span class="sd">/** @Field(type=&quot;string&quot;) */</span>
<span class="k">private</span> <span class="nv">$type</span><span class="p">;</span>
<span class="sd">/** @Field(type=&quot;date&quot;) */</span>
<span class="k">private</span> <span class="nv">$date</span><span class="p">;</span>
<span class="sd">/** @Field(type=&quot;string&quot;) */</span>
<span class="k">private</span> <span class="nv">$description</span><span class="p">;</span>
<span class="c1">// getters and setters</span>
<span class="p">}</span>
<span class="sd">/** @Document */</span>
<span class="k">class</span> <span class="nc">User</span>
<span class="p">{</span>
<span class="c1">// ...</span>
<span class="p">}</span>
</pre></div>
</div>
<p>We may have a situation where we want to run a query that tells us how many
sales events each user has had. We can easily use the map reduce functionality
of MongoDB via the ODM's query builder. Here is a simple map reduce example:</p>
<div class="highlight-php"><div class="highlight"><pre><span class="cp">&lt;?php</span>
<span class="nv">$qb</span> <span class="o">=</span> <span class="nv">$dm</span><span class="o">-&gt;</span><span class="na">createQueryBuilder</span><span class="p">(</span><span class="s1">&#39;Documents\User&#39;</span><span class="p">)</span>
<span class="o">-&gt;</span><span class="na">field</span><span class="p">(</span><span class="s1">&#39;type&#39;</span><span class="p">)</span>
<span class="o">-&gt;</span><span class="na">equals</span><span class="p">(</span><span class="s1">&#39;sale&#39;</span><span class="p">)</span>
<span class="o">-&gt;</span><span class="na">map</span><span class="p">(</span><span class="s1">&#39;function() { emit(this.user.$id, 1); }&#39;</span><span class="p">)</span>
<span class="o">-&gt;</span><span class="na">reduce</span><span class="p">(</span><span class="s1">&#39;function(k, vals) {</span>
<span class="s1"> var sum = 0;</span>
<span class="s1"> for (var i in vals) {</span>
<span class="s1"> sum += vals[i];</span>
<span class="s1"> }</span>
<span class="s1"> return sum;</span>
<span class="s1"> }&#39;</span><span class="p">);</span>
<span class="nv">$query</span> <span class="o">=</span> <span class="nv">$qb</span><span class="o">-&gt;</span><span class="na">getQuery</span><span class="p">();</span>
<span class="nv">$results</span> <span class="o">=</span> <span class="nv">$query</span><span class="o">-&gt;</span><span class="na">execute</span><span class="p">();</span>
<span class="k">foreach</span> <span class="p">(</span><span class="nv">$results</span> <span class="k">as</span> <span class="nv">$user</span><span class="p">)</span> <span class="p">{</span>
<span class="nb">printf</span><span class="p">(</span><span class="s2">&quot;User %s had %d sale(s).</span><span class="se">\n</span><span class="s2">&quot;</span><span class="p">,</span> <span class="nv">$user</span><span class="p">[</span><span class="s1">&#39;_id&#39;</span><span class="p">],</span> <span class="nv">$user</span><span class="p">[</span><span class="s1">&#39;value&#39;</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">The query builder also has a <code class="docutils literal"><span class="pre">finalize()</span></code> method, which may be used to
specify a <a class="reference external" href="https://docs.mongodb.com/master/reference/command/mapReduce/#mapreduce-finalize-cmd">finalize function</a> to be executed after the reduce step.</p>
</div>
<p>When using map reduce with Doctrine, the results are not hydrated into objects.
Instead, the raw results are returned directly from MongoDB.</p>
<p>The preceding example is equivalent to executing the following command via the
PHP driver directly:</p>
<div class="highlight-php"><div class="highlight"><pre><span class="cp">&lt;?php</span>
<span class="nv">$db</span> <span class="o">=</span> <span class="nv">$mongoClient</span><span class="o">-&gt;</span><span class="na">selectDB</span><span class="p">(</span><span class="s1">&#39;my_db&#39;</span><span class="p">);</span>
<span class="nv">$map</span> <span class="o">=</span> <span class="k">new</span> <span class="nx">MongoCode</span><span class="p">(</span><span class="s1">&#39;function() { emit(this.user.$id, 1); }&#39;</span><span class="p">);</span>
<span class="nv">$reduce</span> <span class="o">=</span> <span class="k">new</span> <span class="nx">MongoCode</span><span class="p">(</span><span class="s1">&#39;function(k, vals) {</span>
<span class="s1"> var sum = 0;</span>
<span class="s1"> for (var i in vals) {</span>
<span class="s1"> sum += vals[i];</span>
<span class="s1"> }</span>
<span class="s1"> return sum;</span>
<span class="s1">}&#39;</span><span class="p">);</span>
<span class="nv">$result</span> <span class="o">=</span> <span class="nv">$db</span><span class="o">-&gt;</span><span class="na">command</span><span class="p">(</span><span class="k">array</span><span class="p">(</span>
<span class="s1">&#39;mapreduce&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;events&#39;</span><span class="p">,</span>
<span class="s1">&#39;map&#39;</span> <span class="o">=&gt;</span> <span class="nv">$map</span><span class="p">,</span>
<span class="s1">&#39;reduce&#39;</span> <span class="o">=&gt;</span> <span class="nv">$reduce</span><span class="p">,</span>
<span class="s1">&#39;query&#39;</span> <span class="o">=&gt;</span> <span class="k">array</span><span class="p">(</span><span class="s1">&#39;type&#39;</span> <span class="o">=&gt;</span> <span class="s1">&#39;sale&#39;</span><span class="p">),</span>
<span class="p">));</span>
<span class="k">foreach</span> <span class="p">(</span><span class="nv">$result</span><span class="p">[</span><span class="s1">&#39;results&#39;</span><span class="p">]</span> <span class="k">as</span> <span class="nv">$user</span><span class="p">)</span> <span class="p">{</span>
<span class="nb">printf</span><span class="p">(</span><span class="s2">&quot;User %s had %d sale(s).</span><span class="se">\n</span><span class="s2">&quot;</span><span class="p">,</span> <span class="nv">$user</span><span class="p">[</span><span class="s1">&#39;_id&#39;</span><span class="p">],</span> <span class="nv">$user</span><span class="p">[</span><span class="s1">&#39;value&#39;</span><span class="p">]);</span>
<span class="p">}</span>
</pre></div>
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