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

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<phpdoc:classref xml:id="class.mongodbref" 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 MongoDBRef class</title>
 <titleabbrev>MongoDBRef</titleabbrev>

 <partintro>

<!-- {{{ MongoGridfsCursor intro -->
  <section xml:id="mongodbref.intro">
   &reftitle.intro;
   <para>
    This class can be used to create lightweight links between objects in 
    different collections.
   </para>
   <para>
    <emphasis>Motivation</emphasis>: Suppose we need to refer to a document in 
    another collection. The easiest way is to create a field in the current 
    document.  For example, if we had a "people" collection and an "addresses"
    collection, we might want to create a link between each person document and
    an address document:
    <example>
     <title>Linking documents</title>
     <programlisting role="php">
<![CDATA[
<?php

$people = $db->people;
$addresses = $db->addresses;

$myAddress = array("line 1" => "123 Main Street", 
    "line 2" => null,
    "city" => "Springfield",
    "state" => "Vermont",
    "country" => "USA");

// save the address
$addresses->insert($myAddress);

// save a person with a reference to the address
$me = array("name" => "Fred", "address" => $myAddress['_id']);
$people->insert($me);

?>
]]>
     </programlisting>
    </example>
   </para>
   <para>
    Then, later on, we can find the person's address by querying the "addresses"
    collection with the <classname>MongoId</classname> we saved in the "people"
    collection.
   </para>
   <para>
    Suppose now that we have a more general case, where we don't know which
    collection (or even which database) contains the referenced document.  
    <classname>MongoDBRef</classname> is a good choice for this case, as it is a
    common format that all of the drivers and the database understand.
   </para>
   <para>
    If each person had a list of things they liked which could come from
    multiple collections, such as "hobbies", "sports", "books", etc., we could
    use <classname>MongoDBRef</classname>s to keep track of what "like" went
    with what collection:
    <example>
     <title>Creating MongoDBRef links</title>
    <programlisting role="php">
<![CDATA[
<?php

$people = $db->selectCollection("people");

// model trains are in the "hobbies" collection
$trainRef = MongoDBRef::create("hobbies", $modelTrains['_id']);
// soccer is in the "sports" collection
$soccerRef = MongoDBRef::create("sports", $soccer['_id']);

// now we'll know what collections the items in the "likes" array came from when
// we retrieve this document
$people->insert(array("name" => "Fred", "likes" => array($trainRef, $soccerRef)));

?>
]]>
     </programlisting>
    </example>
   </para>
   <para>
    Database references can be thought of as hyperlinks: they give the unique 
    address of another document, but they do not load it or automatically follow
    the link/reference.  
   </para>
   <para>
    A database reference is just a normal associative array, not an instance of
    <classname>MongoDBRef</classname>, so this class is a little different than 
    the other data type classes.  This class contains exclusively static methods 
    for manipulating database references.
   </para>
  </section>
<!-- }}} -->

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

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

<!-- {{{ Class synopsis -->
    <classsynopsisinfo>
     <ooclass>
      <classname>MongoDBRef</classname>
     </ooclass>
    </classsynopsisinfo>
<!-- }}} -->
    
    <classsynopsisinfo role="comment">&Methods;</classsynopsisinfo>
    <xi:include xpointer="xmlns(db=http://docbook.org/ns/docbook) xpointer(id('class.mongodbref')/db:refentry/db:refsect1[@role='description']/descendant::db:methodsynopsis[1])" />
   </classsynopsis>
<!-- }}} -->

  </section>

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

 &reference.mongo.entities.mongodbref;

</phpdoc:classref>

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<!--  LocalWords:  trainRef soccerRef MongoDBRef
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