php-doc-en/reference/mongo/mongoid.xml

<?xml version="1.0" encoding="utf-8"?>
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<phpdoc:classref xml:id="class.mongoid" xmlns:phpdoc="http://php.net/ns/phpdoc" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xi="http://www.w3.org/2001/XInclude">

 <title>The MongoId class</title>
 <titleabbrev>MongoId</titleabbrev>

 <partintro>

  <warning>
   &mongo.alternative.class.note;
   <simplelist role="alternatives">
    <member><classname>MongoDB\BSON\ObjectId</classname></member>
   </simplelist>
  </warning>

<!-- {{{ MongoId intro -->
  <section xml:id="mongoid.intro">
   &reftitle.intro;
   <para>
    A unique identifier created for database objects.  If an object is inserted
    into the database without an _id field, an _id field will be added to it
    with a <classname>MongoId</classname> instance as its value.  If the data 
    has a naturally occuring unique field (e.g. username or timestamp) it is
    fine to use this as the _id field instead, and it will not be replaced with 
    a <classname>MongoId</classname>.
   </para>
   <para>
    Instances of the <classname>MongoId</classname> class fulfill the role that 
    autoincrementing does in a relational database: to provide a unique key if 
    the data does not naturally have one. Autoincrementing does not work well 
    with a sharded database, as it is difficult to determine the next number in
    the sequence. This class fulfills the constraints of quickly generating a
    value that is unique across shards.
   </para>
   <para>
    Each MongoId is 12 bytes (making its string form 24 hexadecimal characters).
    The first four bytes are a timestamp, the next three are a hash of the
    client machine's hostname, the next two are the two least significant bytes
    of the process id running the script, and the last three bytes are an
    incrementing value.
   </para>
   <para>
    <classname>MongoId</classname>s are serializable/unserializable.  Their
    serialized form is similar to their string form:
    <screen>
<![CDATA[
C:7:"MongoId":24:{4af9f23d8ead0e1d32000000}
]]>
    </screen>
   </para>
  </section>
<!-- }}} -->

  <section xml:id="mongoid.synopsis">
   &reftitle.classsynopsis;

<!-- {{{ Synopsis -->
   <classsynopsis>
    <ooclass><classname>MongoId</classname></ooclass>

<!-- {{{ Class synopsis -->
    <classsynopsisinfo>
     <ooclass>
      <classname>MongoId</classname>
     </ooclass>
    </classsynopsisinfo>
<!-- }}} -->

    <fieldsynopsis>
     <modifier>public</modifier>
     <type>string</type>
     <varname linkend="mongoid.props.id">$id</varname>
     <initializer>&null;</initializer>
    </fieldsynopsis>
    
    <classsynopsisinfo role="comment">&Methods;</classsynopsisinfo>
    <xi:include xpointer="xmlns(db=http://docbook.org/ns/docbook) xpointer(id('class.mongoid')/db:refentry/db:refsect1[@role='description']/descendant::db:methodsynopsis[1])" />
   </classsynopsis>
<!-- }}} -->

  </section>

  <section>
   <title>Fields</title>
   <variablelist>
    <varlistentry xml:id="mongoid.props.id">
     <term><varname>$id</varname></term>
     <listitem>
      <simpara>
       This field contains the string representation of this object.
      </simpara>
      <note>
        <simpara>
          The property name begins with a <literal>$</literal> character. It may
          be accessed using
          <link linkend="language.types.string.parsing.complex">complex variable
          parsed syntax</link> (e.g. <literal>$mongoId->{'$id'}</literal>).
        </simpara>
      </note>
     </listitem>
    </varlistentry>
   </variablelist>
  </section>

  <section>
   &reftitle.seealso;
   <para>
    MongoDB core docs on <link xlink:href="&url.mongodb.dochub.objectids;">ObjectIds</link>.
   </para>
  </section>
 </partintro>

 &reference.mongo.entities.mongoid;

</phpdoc:classref>

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