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

<?xml version="1.0" encoding="utf-8"?>

<!-- $Revision$ -->
<phpdoc:classref xml:id="class.mongocursor" 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 MongoCursor class</title>
 <titleabbrev>MongoCursor</titleabbrev>

 <partintro>

  <!-- {{{ Mongocursor intro -->
  <section xml:id="mongocursor.intro">
   &reftitle.intro;
   <para>
    A cursor is used to iterate through the results of a database query.  For 
    example, to query the database and see all results, you could do:
    <programlisting role="php">
<![CDATA[
<?php

$cursor = $collection->find();
var_dump(iterator_to_array($cursor));

?>
]]>
    </programlisting>
   </para>
   <para>
    You don't generally create cursors using the 
    <classname>MongoCursor</classname> constructor, you get a new cursor by
    calling <function>MongoCollection::find</function> (as shown above).
   </para>
   <para>
    Suppose that, in the example above, <literal>$collection</literal> was a
    50GB collection.  We certainly wouldn't want to load that into memory all 
    at once, which is what a cursor is for: allowing the client to access the 
    collection in dribs and drabs.  
   </para>
   <para>
    If we have a large result set, we can iterate through it, loading a few 
    megabytes of results into memory at a time.  For example, we could do:
    <programlisting role="php">
<![CDATA[
<?php

$cursor = $collection->find();

foreach ($cursor as $doc) {
    // do something to each document
}

?>
]]>
    </programlisting>
    This will go through each document in the collection, loading and garbage 
    collecting documents as needed.
   </para>
   <para>
    Note that this means that a cursor does not "contain" the database results, 
    it just manages them.  Thus, if you print a cursor (with, say, 
    <function>var_dump</function> or <function>print_r</function>), you'll just 
    get the cursor object, not your documents.  To get the documents themselves, 
    you can use one of the methods shown above.
   </para>
  </section>

  <section>
   <title>Cursor Stages</title>
   <para>
    A <classname>MongoCursor</classname> has two "life stages": pre- and post-
    query. When a cursor is created, it has not yet contacted the database, so 
    it is in its pre-query state.  In this state, the client can further specify
    what they want the query to do, including adding limits, skips, sorts, and 
    more advanced options.
   </para>
   <para>
    When the client attempts to get a result (by calling 
    <function>MongoCursor::next</function>, directly or indirectly), the cursor
    moves into the post-query stage.  At this point, the query has been executed
    by the database and cannot be modified anymore.
   </para>
   <para>
    <programlisting role="php">
<![CDATA[
<?php

$cursor = $collection->find()->limit(10);

// database has not yet been queried, so more search options can be added
$cursor = $cursor->sort(array("a" => 1));

var_dump($cursor->getNext());
// now database has been queried and more options cannot be added

// so this will throw an exception:
$cursor->skip(4);
?>
]]>
    </programlisting>
   </para>
  </section>
  <!-- }}} -->

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

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

    <!-- {{{ Class synopsis -->
    <classsynopsisinfo>
     <ooclass>
      <classname>MongoCursor</classname>
     </ooclass>
     <oointerface>
      <interfacename>Iterator</interfacename>
     </oointerface>
    </classsynopsisinfo>
    <!-- }}} -->
    
    <classsynopsisinfo role="comment">Static Fields</classsynopsisinfo>
    <fieldsynopsis>
     <modifier>static</modifier>
     <type>boolean</type>
     <varname linkend="mongocursor.props.slaveokay">slaveOkay</varname>
     <initializer>&false;</initializer>
    </fieldsynopsis>
    <fieldsynopsis>
     <modifier>static</modifier>
     <type>integer</type>
     <varname linkend="mongocursor.props.timeout">timeout</varname>
     <initializer>20000</initializer>
    </fieldsynopsis>

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

  </section>

  <section>
   <title>Static Variables</title>

   <variablelist>
    <varlistentry xml:id="mongocursor.props.slaveokay">
     <term><varname>slaveOkay</varname></term>
     <listitem>
      <para>
       If the query should have the "slaveOkay" flag set, which allows reads on
       the slave (slaves are, by default, just for backup and unreadable).  Can 
       be overridden with <function>MongoCursor::slaveOkay</function>.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry xml:id="mongocursor.props.timeout">
     <term><varname>timeout</varname></term>
     <listitem>
      <para>
       Set timeout in milliseconds for all database responses.  To wait forever,
       use -1. Can be overridden with <function>MongoCursor::timeout</function>.
       This does not cause the MongoDB server to cancel the operation, it just
       causes the driver to stop waiting for a response and throw a
       MongoCursorTimeoutException.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </section>

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

 </partintro>

 &reference.mongo.entities.mongocursor;

</phpdoc:classref>

<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
indent-tabs-mode:nil
sgml-parent-document:nil
sgml-default-dtd-file:"~/.phpdoc/manual.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
vim600: syn=xml fen fdm=syntax fdl=2 si
vim: et tw=78 syn=sgml
vi: ts=1 sw=1
-->