How-to: Use __sleep() to serialize your class

A lot of people run into this problem, and so did I when I first tried this. To make a long story short, I had a class which I wanted to serialize and store in a session variable. I would serialize the class, but when I would echo the output I’d get this:

N;

This would happen regardless of what was in the class. The class used a ‘magic’ function __sleep() to close the db connection. I had read that serialize() automatically calls __sleep(), but I didn’t know is that __sleep() needed to return an array of properties of the class.

Here is some example code to try out. Use it as is, and then comment out the contents in __sleep().

<?php

class sleep_example {
private $var1 = "george";
public function __construct() {}

public function __sleep() {
return array_keys(get_object_vars($this));
}
}

$obj1 = new sleep_example();
$srlz = serialize($obj1);
echo $srlz;

?>

Hopefully you’ll read this before you waste time googl’ing and looking through PHP Bug reports..

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This entry was posted on Tuesday, March 28th, 2006 at 8:09 pm and is filed under PHP/MySQL, Tutorials. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed. Print this post.