serialize, unserialize, __sleep() and wakeup()

definitions:

Serialization: convert an object into a string (storable representation). The included object (instantiated and assigned to internal members) are included in the string.

Unserialization: convert the string into the original object

Possibile uses: shopping cart serialize (to use after or to save into a db), user session save, object transfer between different applications.

serialize($anyContent)

returns a storable representation of $anyContent

example:

serialize(array("val",array(1,2))); //= a:2:{i:0;s:3:"val";i:1;a:2:{i:0;i:1;i:1;i:2;}

unserialize($serializedString)

returns a php value of a serialized string (made using serialize())

$obj = unserialize(a:2:{i:0;s:3:"val";i:1;a:2:{i:0;i:1;i:1;i:2;});

print_r( $obj );

//Array ([0] => val [1] => Array([0] => 1 [1] => 2 ))

to be more clearly

unserialize(serialize($anyContent))

it's equal to

$anyContent

when is the serialization useful ? some example:

• $_SESSION
• db connection handlers
• in general: save object content

PHP5 offers magic methods to serialize and unserialize objects

__sleep() and __wakeup()

Considering the object $classObject:

• __sleep() is automatically called before serialize($classObject) is invoked.
  It returns an array contains the name of the members to serialize.
  Note: the behavior indicated in the official php documentation is different from the result I've obtained in php 5.2.8: every member is serialized, the returning array is ignored !
• __wakeup() is automatically called when we invoke unserialize($classObject)
  It should return and object

class Product
{
public $name;
public $quantity;
public function __construct($name, $quantity) {
$this->name = $name;
$this->quantity = $quantity;
}
}

class ShopCart
{
private $userID = "abc123";
public $products = array( );
public function __construct()
{ //insert some default products
$this->products[0] = new Product("pencil", 3);
$this->products[1] = new Product("pen", 5);
}

public function __sleep()
{
//no userID returned
return array("products");
}
}

$s = new ShopCart();
//print $s->products[1]->quantity."\n"; //5
$s2 = unserialize(serialize($s));

var_dump($s2);
/*
object(ShopCart)#4 (2) {
["userID:private"]=>
string(6) "abc123" // ???????????????????
["products"]=>
array(2) {
[0]=>
object(Product)#5 (2) {
["name"]=>
string(6) "pencil"
["quantity"]=>
int(3)
}
[1]=>
object(Product)#6 (2) {
["name"]=>
string(3) "pen" // ???????????????????
["quantity"]=>
int(5)
}
}
}
*/