__serialize and __unserialize in PHP

Introduction

These methods help you control how an object is saved and restored. They let you decide what data to keep when saving an object and how to rebuild it later.

When you want to save an object to a file or send it over the internet.

When you need to customize which parts of an object are saved.

When restoring an object and you want to set up extra things after loading.

When you want to avoid saving sensitive or unnecessary data.

When you want to improve performance by saving only important data.

Syntax

PHP

class ClassName {
    public function __serialize(): array {
        // return array of data to save
    }

    public function __unserialize(array $data): void {
        // restore object from $data
    }
}

The __serialize method returns an array of data to save.

The __unserialize method receives that array to rebuild the object.

Examples

This example saves and restores the name and age properties.

PHP

class User {
    private string $name;
    private int $age;

    public function __construct(string $name, int $age) {
        $this->name = $name;
        $this->age = $age;
    }

    public function __serialize(): array {
        return ['name' => $this->name, 'age' => $this->age];
    }

    public function __unserialize(array $data): void {
        $this->name = $data['name'];
        $this->age = $data['age'];
    }
}

This example saves only the token and resets secret when restoring.

PHP

class Session {
    private string $token;
    private string $secret;

    public function __serialize(): array {
        // Only save token, not secret
        return ['token' => $this->token];
    }

    public function __unserialize(array $data): void {
        $this->token = $data['token'];
        $this->secret = 'default'; // reset secret
    }
}

Sample Program

This program creates a Product object, saves it as a string, then restores it back to an object and shows its data.

PHP

<?php
class Product {
    private string $name;
    private float $price;

    public function __construct(string $name, float $price) {
        $this->name = $name;
        $this->price = $price;
    }

    public function __serialize(): array {
        return ['name' => $this->name, 'price' => $this->price];
    }

    public function __unserialize(array $data): void {
        $this->name = $data['name'];
        $this->price = $data['price'];
    }

    public function display(): void {
        echo "Product: {$this->name}, Price: \${$this->price}\n";
    }
}

$product = new Product('Book', 12.99);

// Serialize the object
$serialized = serialize($product);
echo "Serialized: $serialized\n";

// Unserialize to new object
$newProduct = unserialize($serialized);
$newProduct->display();

Important Notes

These methods replace older __sleep and __wakeup methods for serialization.

Always return an array from __serialize and accept an array in __unserialize.

Use these methods to avoid saving sensitive data like passwords.

Summary

__serialize controls what data is saved from an object.

__unserialize rebuilds the object from saved data.

They help you save and restore objects safely and efficiently.