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  <div class="section" id="storage-strategies">
<span id="id1"></span><h1>Storage Strategies<a class="headerlink" href="#storage-strategies" title="Permalink to this headline">¶</a></h1>
<p>Doctrine MongoDB ODM implements several different strategies for persisting changes
to mapped fields. These strategies apply to the following mapping types:</p>
<ul class="simple">
<li><span class="xref std std-ref">int</span></li>
<li><span class="xref std std-ref">float</span></li>
<li><a class="reference internal" href="embedded-mapping.html#embed-many"><span class="std std-ref">Embed Many</span></a></li>
<li><a class="reference internal" href="reference-mapping.html#reference-many"><span class="std std-ref">Reference Many</span></a></li>
</ul>
<p>For collections, Doctrine tracks changes via the PersistentCollection class. The
strategies described on this page are implemented by the CollectionPersister
class. The <code class="docutils literal"><span class="pre">increment</span></code> strategy cannot be used for collections.</p>
<div class="section" id="increment">
<h2>increment<a class="headerlink" href="#increment" title="Permalink to this headline">¶</a></h2>
<p>The <code class="docutils literal"><span class="pre">increment</span></code> strategy does not apply to collections but can be used for
<code class="docutils literal"><span class="pre">int</span></code> and <code class="docutils literal"><span class="pre">float</span></code> fields. When using the <code class="docutils literal"><span class="pre">increment</span></code> strategy, the field
value will be updated using the <a class="reference external" href="https://docs.mongodb.com/manual/reference/operator/update/inc/">$inc</a> operator.</p>
</div>
<div class="section" id="addtoset">
<h2>addToSet<a class="headerlink" href="#addtoset" title="Permalink to this headline">¶</a></h2>
<p>The <code class="docutils literal"><span class="pre">addToSet</span></code> strategy uses MongoDB's <a class="reference external" href="https://docs.mongodb.com/manual/reference/operator/update/addToSet/">$addToSet</a> operator to insert
elements into the array. This strategy is useful for ensuring that duplicate
values will not be inserted into the collection. Like the <a class="reference internal" href="#pushall">pushAll</a> strategy,
elements are inserted in a separate query after removing deleted elements.</p>
</div>
<div class="section" id="set">
<h2>set<a class="headerlink" href="#set" title="Permalink to this headline">¶</a></h2>
<p>The <code class="docutils literal"><span class="pre">set</span></code> strategy uses MongoDB's <a class="reference external" href="https://docs.mongodb.com/manual/reference/operator/update/set/">$set</a> operator to update the entire
collection with a single update query.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Doctrine's Collection interface is modeled after PHP's associative arrays,
so they cannot always be represented as a BSON array. If the collection's
keys are not sequential integers starting with zero, the <code class="docutils literal"><span class="pre">set</span></code> strategy
will store the collection as a BSON object instead of an array. Use the
<a class="reference internal" href="#setarray">setArray</a> strategy if you want to ensure that the collection is always
stored as a BSON array.</p>
</div>
</div>
<div class="section" id="setarray">
<h2>setArray<a class="headerlink" href="#setarray" title="Permalink to this headline">¶</a></h2>
<p>The <code class="docutils literal"><span class="pre">setArray</span></code> strategy uses MongoDB's <a class="reference external" href="https://docs.mongodb.com/manual/reference/operator/update/set/">$set</a> operator, just like the <code class="docutils literal"><span class="pre">set</span></code>
strategy, but will first numerically reindex the collection to ensure that it is
stored as a BSON array.</p>
</div>
<div class="section" id="pushall">
<h2>pushAll<a class="headerlink" href="#pushall" title="Permalink to this headline">¶</a></h2>
<p>The <code class="docutils literal"><span class="pre">pushAll</span></code> strategy uses MongoDB's <a class="reference external" href="https://docs.mongodb.com/manual/reference/operator/update/pushAll/">$pushAll</a> operator to insert
elements into the array. MongoDB does not allow elements to be added and removed
from an array in a single operation, so this strategy relies on multiple update
queries to remove and insert elements (in that order).</p>
</div>
<div class="section" id="atomicset">
<span id="atomic-set"></span><h2>atomicSet<a class="headerlink" href="#atomicset" title="Permalink to this headline">¶</a></h2>
<p>The <code class="docutils literal"><span class="pre">atomicSet</span></code> strategy uses MongoDB's <a class="reference external" href="https://docs.mongodb.com/manual/reference/operator/update/set/">$set</a> operator to update the entire
collection with a single update query. Unlike with <code class="docutils literal"><span class="pre">set</span></code> strategy there will
be only one query for updating both parent document and collection itself. This
strategy can be especially useful when dealing with high concurrency and
<a class="reference internal" href="annotations-reference.html#annotations-reference-version"><span class="std std-ref">versioned documents</span></a>.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The <code class="docutils literal"><span class="pre">atomicSet</span></code> and <code class="docutils literal"><span class="pre">atomicSetArray</span></code> strategies may only be used for
collections mapped directly in a top-level document.</p>
</div>
</div>
<div class="section" id="atomicsetarray">
<span id="atomic-set-array"></span><h2>atomicSetArray<a class="headerlink" href="#atomicsetarray" title="Permalink to this headline">¶</a></h2>
<p>The <code class="docutils literal"><span class="pre">atomicSetArray</span></code> strategy works exactly like <code class="docutils literal"><span class="pre">atomicSet</span></code> strategy,  but
will first numerically reindex the collection to ensure that it is stored as a
BSON array.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The <code class="docutils literal"><span class="pre">atomicSet</span></code> and <code class="docutils literal"><span class="pre">atomicSetArray</span></code> strategies may only be used for
collections mapped directly in a top-level document.</p>
</div>
</div>
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            <h3><a href="../index.html">Table Of Contents</a></h3>
            <ul>
<li><a class="reference internal" href="#">Storage Strategies</a><ul>
<li><a class="reference internal" href="#increment">increment</a></li>
<li><a class="reference internal" href="#addtoset">addToSet</a></li>
<li><a class="reference internal" href="#set">set</a></li>
<li><a class="reference internal" href="#setarray">setArray</a></li>
<li><a class="reference internal" href="#pushall">pushAll</a></li>
<li><a class="reference internal" href="#atomicset">atomicSet</a></li>
<li><a class="reference internal" href="#atomicsetarray">atomicSetArray</a></li>
</ul>
</li>
</ul>

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