PDOException: You cannot serialize or unserialize PDO instances

Question

I tried to cache my User object in PHP with memcache, but I get an error while using PDO. I added a __sleep and a __wakeup function.

User.php

/**
 * @var PDO
 */
protected $db;

public function __construct()
{
    $this->db = getInstanceOf('db');
}

public function __destruct()
{

}

public function __sleep()
{
    return array('db');
}

public function __wakeup()
{
    $this->db = getInstanceOf('db');
}

getInstanceOf('db') returns a pdo object...

Returns the following error:

PDOException: You cannot serialize or unserialize PDO instances in /var/www/test/User.php on line 41

Answer 1

It is likely that $this->db is a PDO object. PDO objects can not be serialized.

Remove that object on __sleep() and add it back at __wakeup() (which is what you already do in the later case):

public function __sleep()
{
    return array();
}

You can not serialize objects that can not be serialized. But you tried, so you got the exception. That's basically the whole issue. Just don't tell PHP to serialize objects that can't be serialized.