__serialize and __unserialize in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the __serialize method that returns the object's data as an array.

PHP

<?php
class User {
    private $name;
    private $age;

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

    public function __serialize(): array {
        return [1];
    }
}
?>

Drag options to blanks, or click blank then click option'

Aarray("name" => $this->name, "age" => $this->age)

B["name" => $this->name, "age" => $this->age]

C[$this->name, $this->age]

Dserialize($this)

Attempts:

3 left

💡 Hint

Common Mistakes

Returning a serialized string instead of an array.

Returning a numeric array without keys.

The __serialize method must return an array of the object's data. Using array() syntax is correct here.

2fill in blank

medium

Complete the code to define the __unserialize method that restores the object's properties from the given data array.

PHP

<?php
class User {
    private $name;
    private $age;

    public function __unserialize(array $data): void {
        $this->name = $data[[1]];
        $this->age = $data["age"];
    }
}
?>

Drag options to blanks, or click blank then click option'

A1

B"name"

C0

D"age"

Attempts:

3 left

💡 Hint

Common Mistakes

Using numeric indexes instead of string keys.

Mixing up keys for name and age.

The __unserialize method receives an array with keys matching the property names. So to restore $name, use the key "name".

3fill in blank

hard

Fix the error in the __serialize method to correctly return the object's data as an array.

PHP

<?php
class Product {
    private $id;
    private $price;

    public function __serialize(): array {
        return [1];
    }
}
?>

Drag options to blanks, or click blank then click option'

Aarray("id", $this->id, "price", $this->price)

Bserialize(["id" => $this->id, "price" => $this->price])

C["id" => $this->id, "price" => $this->price]

D[$this->id, $this->price]

Attempts:

3 left

💡 Hint

Common Mistakes

Returning a serialized string instead of an array.

Returning a numeric array without keys.

The __serialize method must return an associative array with keys and values, not a serialized string or a numeric array.

4fill in blank

hard

Fill both blanks to complete the __unserialize method that restores the object's properties from the data array.

PHP

<?php
class Product {
    private $id;
    private $price;

    public function __unserialize(array $data): void {
        $this->id = $data[[1]];
        $this->price = $data[[2]];
    }
}
?>

Drag options to blanks, or click blank then click option'

A"id"

B"price"

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using numeric indexes instead of string keys.

Swapping the keys for id and price.

The __unserialize method uses the keys "id" and "price" to restore the respective properties from the data array.

5fill in blank

hard

Fill all three blanks to complete the class with __serialize and __unserialize methods that handle the properties correctly.

PHP

<?php
class Book {
    private $title;
    private $author;
    private $pages;

    public function __serialize(): array {
        return [[1] => $this->title, [2] => $this->author, [3] => $this->pages];
    }

    public function __unserialize(array $data): void {
        $this->title = $data["title"];
        $this->author = $data["author"];
        $this->pages = $data["pages"];
    }
}
?>

Drag options to blanks, or click blank then click option'

A"title"

B"author"

C"pages"

D"book"

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect or inconsistent keys.

Using a single key for all properties.

The __serialize method returns an associative array with keys matching the property names: "title", "author", and "pages".

Practice

1. What is the main purpose of the __serialize method in a PHP class?

easy

A. To specify which object properties should be saved during serialization

B. To automatically convert an object to a string

C. To rebuild an object from saved data

D. To delete object properties before saving

Solution

1. Step 1: Understand serialization

   Serialization means saving an object's data so it can be stored or sent.

2. Step 2: Role of __serialize

   The __serialize method tells PHP which properties to save when serializing.

3. Final Answer:

   To specify which object properties should be saved during serialization -> Option A

4. Quick Check:

   __serialize controls saved data = A [OK]

Hint: Remember: __serialize picks what to save [OK]

Common Mistakes:

• Confusing __serialize with __unserialize
• Thinking __serialize rebuilds objects
• Assuming it converts objects to strings automatically

2. Which of the following is the correct syntax for defining the __unserialize method in a PHP class?

easy

A. public function __unserialize($data)

B. function __unserialize(): array

C. private function __unserialize(array $data): string

D. public function __unserialize(array $data): void

Solution

1. Step 1: Check method signature

   The __unserialize method must accept an array parameter and return nothing (void).

2. Step 2: Match correct syntax

   public function __unserialize(array $data): void matches the correct signature: public function __unserialize(array $data): void.

3. Final Answer:

   public function __unserialize(array $data): void -> Option D

4. Quick Check:

   __unserialize signature = B [OK]

Hint: Look for array parameter and void return [OK]

Common Mistakes:

• Missing type hint for parameter
• Wrong return type specified
• Using private instead of public visibility

3. What will be the output of the following PHP code?

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];
    }

    public function __unserialize(array $data): void {
        $this->name = $data['name'];
        $this->age = 0;
    }

    public function getInfo(): string {
        return "Name: {$this->name}, Age: {$this->age}";
    }
}

$user = new User('Alice', 30);
$serialized = serialize($user);
$unserialized = unserialize($serialized);
echo $unserialized->getInfo();

medium

A. Name: Alice, Age: 30

B. Name: Alice, Age: 0

C. Name: , Age: 0

D. Error: Undefined index 'name'

Solution

1. Step 1: Analyze __serialize output

   The __serialize method returns only the 'name' property, so 'age' is not saved.

2. Step 2: Analyze __unserialize behavior

   When unserializing, 'name' is restored from data, but 'age' is set to 0 explicitly.

3. Final Answer:

   Name: Alice, Age: 0 -> Option B

4. Quick Check:

   Only 'name' saved, 'age' reset = C [OK]

Hint: Check what __serialize returns and how __unserialize sets properties [OK]

Common Mistakes:

• Assuming all properties are saved automatically
• Expecting original age to be restored
• Ignoring explicit age reset in __unserialize

4. Identify the error in this PHP class using __serialize and __unserialize:

class Product {
    private string $title;
    private float $price;

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

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

medium

A. Properties should be public for serialization

B. Missing return type in __serialize method

C. Using 'cost' key in __unserialize instead of 'price'

D. No constructor defined

Solution

1. Step 1: Compare keys in __serialize and __unserialize

   The __serialize method saves 'price' key, but __unserialize tries to read 'cost' key.

2. Step 2: Identify mismatch impact

   This mismatch causes an undefined index error when unserializing.

3. Final Answer:

   Using 'cost' key in __unserialize instead of 'price' -> Option C

4. Quick Check:

   Key mismatch in serialize/unserialize = A [OK]

Hint: Match keys exactly between __serialize and __unserialize [OK]

Common Mistakes:

• Using different keys for same property
• Ignoring array keys case sensitivity
• Assuming missing keys won't cause errors

5. You want to securely save only non-sensitive user data from an object and restore it later. Which approach using __serialize and __unserialize is best?

hard

A. In __serialize, return only non-sensitive properties; in __unserialize, restore those and set sensitive ones to defaults

B. Serialize all properties automatically and trust the storage security

C. Use __serialize to encrypt all data and __unserialize to decrypt

D. Do not implement __serialize or __unserialize and rely on default serialization

Solution

1. Step 1: Understand security needs

   Only non-sensitive data should be saved to avoid leaks.

2. Step 2: Use __serialize and __unserialize properly

   Return only safe properties in __serialize and restore them in __unserialize, setting sensitive data to safe defaults.

3. Final Answer:

   In __serialize, return only non-sensitive properties; in __unserialize, restore those and set sensitive ones to defaults -> Option A

4. Quick Check:

   Selective save and safe restore = D [OK]

Hint: Save only safe data, reset sensitive on restore [OK]

Common Mistakes:

• Saving all data without filtering
• Assuming encryption happens automatically
• Ignoring sensitive data in unserialize