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The magic method __sleep() and __wakeup() is called when an object is serialized. The magic method __sleep() and __wakeup() provides a method to clean up and restore objects before being serialized.

Working with the magic method __sleep()

__sleep() magic method is called when the object of a class is about to be serialized. This magic method __sleep() does not accept any parameter and returns an array. The array should contain a list of class members that should be serialized. This means that if you don’t wish to serialize a particular class member, you should not include it in the array. Look at the example below:

class Customer {
	private $name;
	private $credit_card_number;
 
	public function setName($name) {
		$this->name = $name;
	}
 
	public function getName() {
		return $this->name;
	}
 
	public function setCC($cc) {
		$this->credit_card_number = $cc;
	}
 
	public function getCC() {
		return $this->credit_card_number;
	}
 
	public function __sleep() {
		return array("name"); //because of this, only name is serialized
	}
 
}
 
$c = new Customer();
$c->setName("Sunil");
$c->setCC("1234567890123456");
 
$data = serialize($c)."\n";
echo $data."\n";

Output:
O:8:”Customer”:1:{s:14:” Customer name”;s:5:”Sunil”;}

In the above example, you can see that the serialized string data only contains the name of the Customer Object. This is because the __sleep() magic method returned an array containing only the ‘name’ data member.

Working with the magic method __wakeup()

__wakeup() magic method is the opposite of the __sleep() method. It is called when the object of a class is about to be unserialized. This magic method __wakeup() does not accept any parameter nor returns anything. The __wakeup() method is responsible for setup operations after an object has been unserialized. Look at the example below:

class Customer {
	private $name;
	private $credit_card_number;
 
	public function setName($name) {
		$this->name = $name;
	}
 
	public function getName() {
		return $this->name;
	}
 
	public function setCC($cc) {
		$this->credit_card_number = $cc;
	}
 
	public function getCC() {
		return $this->credit_card_number;
	}
 
	public function __sleep() {
		return array("name");
	}
 
	public function __wakeup() {
		if($this->name == "Sunil") {
			//you would ideally fetch CC data from Database
			$this->credit_card_number = "1234567890123456";
		}
	}
}
 
$c = new Customer();
$c->setName("Sunil");
$c->setCC("1234567890123456");
 
$data = serialize($c)."\n";
var_dump(unserialize($data));

Output:
object(Customer)#2 (2) {
[”name:private”]=>
string(5) “Sunil”
[”credit_card_number:private”]=>
string(16) “1234567890123456″
}

In the above example, you can see that after the $c object has been serialized and the output stored in $data variable, we use the $data variable and pass it to the unserialize(). Before the object is unserizlied and object created, the __wakeup() method is called. In the __wakeup() method you should ideally make a database call to fetch data of the missing member variable.

Please feel free to leave behind any comments or questions that you might have.

Related Posts on PHP5 Tutorial - Object Oriented Programming (OOPS)

1. PHP5 Tutorial - Learn to create a PHP5 Class
2. PHP5 Tutorial - Learn to Create a PHP5 Class Object
3. PHP5 Tutorial - Defining Attributes of a PHP5 Class
4. PHP5 Tutorial - Defining Methods of a PHP5 Class
5. PHP5 Tutorial - Creating a PHP5 Constructor __construct()
6. PHP5 Tutorial OOPS - Creating a PHP5 Destructor __destruct()
7. PHP5 Tutorial OOPS - PHP5 Class Access Specifiers - public, private and protected
8. PHP5 Tutorial - Magic Methods - __toString() method
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11. PHP5 Tutorial - Magic Methods - __call() method
12. PHP5 Tutorial - Magic Methods - __autoload() method
13. PHP5 Tutorial - Magic Methods - __sleep() and __wakeup()
14. PHP5 Tutorial - Magic Methods - __clone() method

Filed under: PHP, PHP Tutorials, PHP5 Magic Methods, PHP5 OOPS Tutorials