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<title>The MongoDB\BSON\ObjectId class</title>
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<h1 class="title">The MongoDB\BSON\ObjectId class</h1>
<div class="partintro"><p class="verinfo">(mongodb >=1.0.0)</p>
<div class="section" id="mongodb-bson-objectid.intro">
<h2 class="title">Introduction</h2>
<p class="para">
BSON type for an
<a href="https://docs.mongodb.com/manual/reference/bson-types/#objectid" class="link external">» ObjectId</a>. The
value consists of 12 bytes, where the first four bytes are a timestamp
that reflect the ObjectId's creation. Specifically, the value consists of:
</p>
<ul class="itemizedlist">
<li class="listitem"><span class="simpara">a 4-byte value representing the seconds since the Unix epoch,</span></li>
<li class="listitem"><span class="simpara">a 3-byte machine identifier,</span></li>
<li class="listitem"><span class="simpara">a 2-byte process ID, and</span></li>
<li class="listitem"><span class="simpara">a 3-byte counter, starting with a random value.</span></li>
</ul>
<p class="para">
In MongoDB, each document stored in a collection requires a unique
<em>_id</em> field that acts as a primary key. If an inserted
document omits the <em>_id</em> field, the driver automatically
generates an ObjectId for the <em>_id</em> field.
</p>
<p class="para">
Using ObjectIds for the <em>_id</em> field provides the following
additional benefits:
</p>
<ul class="itemizedlist">
<li class="listitem"><span class="simpara">The creation time of the ObjectId may be accessed using the <span class="methodname"><a href="mongodb-bson-objectid.gettimestamp.html" class="methodname">MongoDB\BSON\ObjectId::getTimestamp()</a></span> method.</span></li>
<li class="listitem"><span class="simpara">Sorting on an <em>_id</em> field that stores ObjectId values is roughly equivalent to sorting by creation time.</span></li>
</ul>
</div>
<div class="section" id="mongodb-bson-objectid.synopsis">
<h2 class="title">Class synopsis</h2>
<div class="classsynopsis">
<div class="ooclass"></div>
<div class="classsynopsisinfo">
<span class="modifier">final</span>
<span class="ooclass">
<strong class="classname">MongoDB\BSON\ObjectId</strong>
</span>
<span class="oointerface">implements
<span class="interfacename"><a href="class.mongodb-bson-objectidinterface.html" class="interfacename">MongoDB\BSON\ObjectIdInterface</a></span>
</span>
<span class="oointerface">,
<span class="interfacename"><a href="class.mongodb-bson-type.html" class="interfacename">MongoDB\BSON\Type</a></span>
</span>
<span class="oointerface">,
<span class="interfacename"><a href="class.serializable.html" class="interfacename">Serializable</a></span>
</span>
<span class="oointerface">,
<span class="interfacename"><a href="class.jsonserializable.html" class="interfacename">JsonSerializable</a></span>
</span>
{</div>
<div class="classsynopsisinfo classsynopsisinfo_comment">/* Methods */</div>
<div class="methodsynopsis dc-description">
<span class="modifier">final</span> <span class="modifier">public</span> <span class="methodname"><a href="mongodb-bson-objectid.construct.html" class="methodname">__construct</a></span>
([ <span class="methodparam"><span class="type">string</span> <code class="parameter">$id</code></span>
] )</div>
<div class="methodsynopsis dc-description">
<span class="modifier">final</span> <span class="modifier">public</span> <span class="type">int</span> <span class="methodname"><a href="mongodb-bson-objectid.gettimestamp.html" class="methodname">getTimestamp</a></span>
( <span class="methodparam">void</span>
)</div>
<div class="methodsynopsis dc-description">
<span class="modifier">final</span> <span class="modifier">public</span> <span class="type">mixed</span> <span class="methodname"><a href="mongodb-bson-objectid.jsonserialize.html" class="methodname">jsonSerialize</a></span>
( <span class="methodparam">void</span>
)</div>
<div class="methodsynopsis dc-description">
<span class="modifier">final</span> <span class="modifier">public</span> <span class="type">string</span> <span class="methodname"><a href="mongodb-bson-objectid.serialize.html" class="methodname">serialize</a></span>
( <span class="methodparam">void</span>
)</div>
<div class="methodsynopsis dc-description">
<span class="modifier">final</span> <span class="modifier">public</span> <span class="type">string</span> <span class="methodname"><a href="mongodb-bson-objectid.tostring.html" class="methodname">__toString</a></span>
( <span class="methodparam">void</span>
)</div>
<div class="methodsynopsis dc-description">
<span class="modifier">final</span> <span class="modifier">public</span> <span class="type">void</span> <span class="methodname"><a href="mongodb-bson-objectid.unserialize.html" class="methodname">unserialize</a></span>
( <span class="methodparam"><span class="type">string</span> <code class="parameter">$serialized</code></span>
)</div>
}</div>
</div>
<div class="section">
<h2 class="title">Changelog</h2>
<p class="para">
<table class="doctable informaltable">
<thead>
<tr>
<th>Version</th>
<th>Description</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td>1.3.0</td>
<td>
<p class="para">
Renamed from <em>MongoDB\BSON\ObjectID</em> to
<em>MongoDB\BSON\ObjectId</em>.
</p>
</td>
</tr>
<tr>
<td>1.2.0</td>
<td>
Implements <span class="interfacename"><a href="class.serializable.html" class="interfacename">Serializable</a></span> and
<span class="interfacename"><a href="class.jsonserializable.html" class="interfacename">JsonSerializable</a></span>.
</td>
</tr>
</tbody>
</table>
</p>
</div>
</div>
<h2>Table of Contents</h2><ul class="chunklist chunklist_reference"><li><a href="mongodb-bson-objectid.construct.html">MongoDB\BSON\ObjectId::__construct</a> — Construct a new ObjectId</li><li><a href="mongodb-bson-objectid.gettimestamp.html">MongoDB\BSON\ObjectId::getTimestamp</a> — Returns the timestamp component of this ObjectId</li><li><a href="mongodb-bson-objectid.jsonserialize.html">MongoDB\BSON\ObjectId::jsonSerialize</a> — Returns a representation that can be converted to JSON</li><li><a href="mongodb-bson-objectid.serialize.html">MongoDB\BSON\ObjectId::serialize</a> — Serialize an ObjectId</li><li><a href="mongodb-bson-objectid.tostring.html">MongoDB\BSON\ObjectId::__toString</a> — Returns the hexidecimal representation of this ObjectId</li><li><a href="mongodb-bson-objectid.unserialize.html">MongoDB\BSON\ObjectId::unserialize</a> — Unserialize an ObjectId</li></ul>
</div>
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