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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<!-- TODO Rewrite to remove usage of "you" and talk about __serialize/_unserialize -->
<sect1 xml:id="language.oop5.serialization" xmlns="http://docbook.org/ns/docbook">
<title>Serializing objects - objects in sessions</title>
<titleabbrev>Object Serialization</titleabbrev>
<para>
<function>serialize</function> returns a string containing a
byte-stream representation of any value that can be stored in
PHP. <function>unserialize</function> can use this string to
recreate the original variable values. Using serialize to
save an object will save all variables in an object. The
methods in an object will not be saved, only the name of
the class.
</para>
<para>
In order to be able to <function>unserialize</function> an object, the
class of that object needs to be defined. That is, if you have an object
of class A and serialize this, you'll
get a string that refers to class A and contains all values of variables
contained in it. If you want to be able to unserialize
this in another file, an object of class A, the
definition of class A must be present in that file first.
This can be done for example by storing the class definition of class A
in an include file and including this file or making use of the
<function>spl_autoload_register</function> function.
</para>
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
// A.php:
class A {
public $one = 1;
public function show_one() {
echo $this->one;
}
}
// page1.php:
include "A.php";
$a = new A;
$s = serialize($a);
// store $s somewhere where page2.php can find it.
file_put_contents('store', $s);
// page2.php:
// this is needed for the unserialize to work properly.
include "A.php";
$s = file_get_contents('store');
$a = unserialize($s);
// now use the function show_one() of the $a object.
$a->show_one();
?>
]]>
</programlisting>
</informalexample>
<para>
It is strongly recommended that if an application serializes objects, for use
later in the application, that the application includes the class definition
for that object throughout the application. Not doing so might result in an
object being unserialized without a class definition, which will result in
PHP giving the object a class of <classname>__PHP_Incomplete_Class_Name</classname>,
which has no methods and would render the object useless.
</para>
<para>
So if in the example above <varname>$a</varname> became part of a session
by adding a new key to the <varname>$_SESSION</varname> superglobal array, you should include the
file <literal>A.php</literal> on all of your pages, not only <filename>page1.php</filename>
and <filename>page2.php</filename>.
</para>
<para>
Beyond the above advice, note that you can also hook into the serialization
and unserialization events on an object using the
<link linkend="object.sleep">__sleep()</link> and
<link linkend="object.wakeup">__wakeup()</link> methods. Using
<link linkend="object.sleep">__sleep()</link> also allows you to only
serialize a subset of the object's properties.
</para>
</sect1>
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