Serializing objects - objects in sessions
Note: In PHP 3, objects will lose their class association
throughout the process of serialization and unserialization.
The resulting variable is of type object, but has no class
and no methods, thus it is pretty useless (it has become just
like an array with a funny syntax).
Caution
The following information is valid for PHP 4 only.
serialize() returns a string containing a byte-stream representation
of any value that can be stored in PHP. unserialize() can
use this string to recreate the original variable values.
Using serialize to save an object will save all variables
in an object. The functions in an object will not be saved,
only the name of the class.
In order to be able to unserialize() an object, the class
of that object needs to be defined. That is, if you have
an object $a of class A on page1.php and serialize this,
you'll get a string that refers to class A and contains
all values of variabled contained in $a. If you want to
be able to unserialize this on page2.php, recreating $a
of class A, the definition of class A must be present in
page2.php. This can be done for example by storing the class
definition of class A in an include file and including this
file in both page1.php and page2.php.
<?php
// classa.inc:
class A {
var $one = 1;
function show_one() {
echo $this->one;
}
}
// page1.php:
include("classa.inc");
$a = new A;
$s = serialize($a);
// store $s somewhere where page2.php can find it.
$fp = fopen("store", "w");
fwrite($fp, $s);
fclose($fp);
// page2.php:
// this is needed for the unserialize to work properly.
include("classa.inc");
$s = implode("", @file("store"));
$a = unserialize($s);
// now use the function show_one() of the $a object.
$a->show_one();
?>
If you are using sessions and use session_register() to
register objects, these objects are serialized automatically
at the end of each PHP page, and are unserialized automatically
on each of the following pages. This basically means that
these objects can show up on any of your pages once they
become part of your session.
It is strongly recommended that you include the class definitions
of all such registered objects on all of your pages, even
if you do not actually use these classes on all of your
pages. If you don't and an object is being unserialized
without its class definition being present, it will lose
its class association and become an object of class stdClass
without any functions available at all, that is, it will
become quite useless.
So if in the example above $a became part of a session
by running session_register("a"), you should include
the file classa.inc on all of your pages, not only page1.php
and page2.php.
