The Serializable interface

(PHP 5 >= 5.1.0, PHP 7, PHP 8)

Introduction

Interface for customized serializing.

Classes that implement this interface no longer support __sleep() and __wakeup(). The method serialize is called whenever an instance needs to be serialized. This does not invoke __destruct() or have any other side effect unless programmed inside the method. When the data is unserialized the class is known and the appropriate unserialize() method is called as a constructor instead of calling __construct(). If you need to execute the standard constructor you may do so in the method.

Warning

As of PHP 8.1.0, a class which implements Serializable without also implementing __serialize() and __unserialize() will generate a deprecation warning.

Interface synopsis

interface Serializable {

/* Methods */

public serialize(): ?string

public unserialize(string $data): void

}

Example #1 Basic usage

<?php
class obj implements Serializable {
    private $data;
    public function __construct() {
        $this->data = "My private data";
    }
    public function serialize() {
        return serialize($this->data);
    }
    public function unserialize($data) {
        $this->data = unserialize($data);
    }
    public function getData() {
        return $this->data;
    }
}

$obj = new obj;
$ser = serialize($obj);

var_dump($ser);

$newobj = unserialize($ser);

var_dump($newobj->getData());
?>

The above example will output something similar to:

string(38) "C:3:"obj":23:{s:15:"My private data";}"
string(15) "My private data"

Serializable::serialize — String representation of object
Serializable::unserialize — Constructs the object

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User Contributed Notes 7 notes

down

grzeniufication ¶

9 years ago


Here's an example how to un-, serialize more than one property:

class Example implements \Serializable
{
    protected $property1;
    protected $property2;
    protected $property3;

    public function __construct($property1, $property2, $property3)
    {
        $this->property1 = $property1;
        $this->property2 = $property2;
        $this->property3 = $property3;
    }

    public function serialize()
    {
        return serialize([
            $this->property1,
            $this->property2,
            $this->property3,
        ]);
    }

    public function unserialize($data)
    {
        list(
            $this->property1,
            $this->property2,
            $this->property3
        ) = unserialize($data);
    }

}

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shaun at slickdesign dot com dot au ¶

6 years ago


Serialized strings differ between instances that implement Serializable and those that don't.

Instances that don't implement Serializable use the Object notation "O:" when serialized, while those that do use the Class notation "C:". Class notation can only be used to unserialize instances that implement Serializable, while the Object notation can be used to unserialize any object.

Because of this, it is sometimes useful to implement the __wakeup() function when implementing Serializable, for instances where you may have a copy of the serialised class before it implemented Serializable (backwards compatible), or when you're expecting a serialized object from an external source, and they use Object notation for maximum compatibility. You can also use __wakeup() to process your unserialize function, or use it to help prevent people trying to bypass your unserialize.

Below is an example of a simple class hierarchy, where A is a standard class, B implements Serializable, and C uses __wakeup() to assist with unserializing it.

<?php
class A {
    protected $readonly_data = true;
    public $public_data = true;
    
    public function __construct( $data = true ) {
        $this->public_data = $data;
    }
    
    public function get_readonly_data() {
        return $this->readonly_data;
    }
}

$a = new A;

var_dump( $a );
//object(A)#1 (2) {
//  ["readonly_data":protected]=>
//  bool(true)
//  ["public_data"]=>
//  bool(true)
//}
var_dump( serialize( $a ) );
//string(63) "O:1:"A":2:{s:16:"*readonly_data";b:1;s:11:"public_data";b:1;}"
?>
Class A outputs the following object, and its serialized string uses the object notation "O:". Please note that there is a null byte "\0" either side of the star*.

Changing the serialised string and unserializing it can cause protected and private values to change.
<?php
var_dump( unserialize( "O:1:\"A\":2:{s:16:\"\0*\0readonly_data\";b:0;s:11:\"public_data\";b:0;}" ) );
//object(A)#1 (2) {
//  ["readonly_data":protected]=>
//  bool(false)
//  ["public_data"]=>
//  bool(false)
//}
?>

Class B extends A, and so has the same constructor and properties. It also implements Serializable.
<?php
class B extends A implements Serializable {
    public function serialize() {
        return serialize( $this->public_data );
    }
    
    public function unserialize( $data ) {
        $this->public_data = unserialize ( $data );
        do_extra_processing_here();
    }
}

$b = new B;

var_dump( serialize( $b ) );
// C:1:"B":4:{b:1;}
?>
As well as being a lot shorter, the serialized string uses the Class notation "C:", but you can still unserialize it using the older style notation. Doing this however will completely ignore the unserialize() function, potentially update the wrong information, and the function do_extra_processing_here() from the example above is not called.
<?php
var_dump( unserialize( "O:1:\"B\":2:{s:16:\"\0*\0readonly_data\";b:0;s:11:\"public_data\";b:0;}" ) );
//object(B)#1 (2) {
//  ["readonly_data":protected]=>
//  bool(false)
//  ["public_data"]=>
//  bool(false)
//}
?>

Class C extends B, so it's already using the serialize() and unserialize() functions. By implementing the __wakeup() method, we ensure that we are validating the information and performing our do_extra_processing_here() function.
<?php
class C extends B {
    public function __wakeup() {
        $new = new static;
        $this->readonly_data = $new->get_readonly_data();
        do_extra_processing_here();
    }
}

var_dump( unserialize( "O:1:\"C\":2:{s:16:\"\0*\0readonly_data\";b:0;s:11:\"public_data\";b:0;}" ) );
//object(B)#1 (2) {
//  ["readonly_data":protected]=>
//  bool(true)
//  ["public_data"]=>
//  bool(false)
//}
?>
We can use __wakeup() to revert our readonly data back to what it was, or to add additional processing. You can additionally call __wakeup() from within unserialize() if you need to do the same process regardless of which serialized string notation was used.

down

info at ensostudio dot ru ¶

4 years ago


Note: that interface declared as "deprecated" in PHP 7.4, use magic methods __serialize() and __unserialize()  instead .

down

marcos dot gottardi at folha dot REM0VE-THIS dot com dot br ¶

12 years ago


Serializing child and parent classes:

<?php
class MyClass implements Serializable {
    private $data;
    
    public function __construct($data) {
        $this->data = $data;
    }
    
    public function getData() {
        return $this->data;
    }
    
    public function serialize() {
        echo "Serializing MyClass...\n";
        return serialize($this->data);
    }
    
    public function unserialize($data) {
        echo "Unserializing MyClass...\n";
        $this->data = unserialize($data);
    }
}

class MyChildClass extends MyClass {
    private $id;
    private $name;
    
    public function __construct($id, $name, $data) {
        parent::__construct($data);
        $this->id = $id;
        $this->name = $name;
    }
    
    public function serialize() {
        echo "Serializing MyChildClass...\n";
        return serialize(
            array(
                'id' => $this->id,
                'name' => $this->name,
                'parentData' => parent::serialize()
            )
        );
    }
    
    public function unserialize($data) {
        echo "Unserializing MyChildClass...\n";
        $data = unserialize($data);
        
        $this->id = $data['id'];
        $this->name = $data['name'];
        parent::unserialize($data['parentData']);
    }
    
    public function getId() {
        return $this->id;
    }
    
    public function getName() {
        return $this->name;
    }
}

$obj = new MyChildClass(15, 'My class name', 'My data');

$serial = serialize($obj);
$newObject = unserialize($serial);

echo $newObject->getId() . PHP_EOL;
echo $newObject->getName() . PHP_EOL;
echo $newObject->getData() . PHP_EOL;

?>

This will output:

Serializing MyChildClass...
Serializing MyClass...
Unserializing MyChildClass...
Unserializing MyClass...
15
My class name
My data

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-8

Olivier Pons ¶

10 years ago


Here's the way you could implement serializable so that *ALL* descendant serialize themselves without the need of re-writing for all descendant the functions serialize() and unserialize().

Note : this will only serialize "visible" properties, this it won't serialize private descendant properties. If you dont want a property of a descendant to be serialized, make it private.

class Pot implements Serializable
{
    protected $_a;
    protected $_b;

    public function serialize()
    {
        return serialize(get_object_vars($this));
    }
    public function unserialize($data)
    {
        $values = unserialize($data);
        foreach ($values as $key=>$value) {
            $this->$key = $value;
        }
    }
}

And now one descendant:

class PotId implements Pot
{
    protected $_k;
}

class Pots implements PotId
{
    protected $_l;
}

$pots = new Pots();

and calling serialize($pots) will serialize all properties ($_a, $_b, $_k, $l).

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-6

Wojciech Brozyna ¶

8 years ago


My solution that let you serialize inherited objects.
Without specify what need to be serialized.
We want to get rid of PDO object in this example.

abstract class DefaultModel() implements \Serializable
{

    /**
    * @var PDO
    */
    private $pdo;

    /**
     * Serialize object
     * 
     * @return string
     */
    public function serialize()
    {
        
        $serializable = get_object_vars($this);
        
        // unset property name that hold PDO instance
        unset($serializable['pdo']);
        
        return serialize($serializable);
        
    }

    /**
     * Unserialize object
     * 
     * @param string $serialized Serialized object
     * @return DefaultModel
     */
    public function unserialize($serialized)
    {
        
        $unserialized = unserialize($serialized);
        
       // recreate PDO object
        $this->pdo = $this->createDBObject();
        
        if(is_array($unserialized) === true) {
            
            foreach($unserialized as $property => $value) {
                
                $this->{$property} = $value;
                
            }
            
        }
        
    }

}

class RealModel extends DefaultModel
{

    private $myVar;

    public function setMyVar($value)
    {

        $this->myVar = $value;

    }

}

$model = new RealModel();
$model->setMyVar('123456');

$serialized = serialize($model);
$serialized = $model->serialize();   // will also work

print_r($serialized);

$unserialized = unserialize($serialized);

print_r($unserialized);

Hope this help.

down

-18

Anonymous ¶

13 years ago


You can prevent an object getting unserialized by returning NULL. Instead of a serialized object, PHP will return the serialized form of NULL:

<?php
class testNull implements Serializable {
    public function serialize() {        
        return NULL;
    }
    public function unserialize($data) {
    }
}

$obj = new testNull;
$string = serialize($obj);
echo $string; // "N;"
?>

That's perhaps better than throwing exceptions inside of the serialize function if you want to prevent serialization of certain objects.

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The Serializable interface

Introduction

Interface synopsis

Table of Contents

User Contributed Notes 7 notes