Factory Method Design Pattern Explained with PHP Examples

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Facetory is a but in Creational Design Patterns, help create object , don't need specify class

Instead of create object using new , Facetory Method using a method special in class or interface ,after then return object

Purpose

Provides flexibility to add new classes without changing existing source code
Increase Scalability (open/closed Principle)
Separate object initialzation logic from main business logic

Factory Method Structure

Product : Interface or abstract class defines the objects that are created
Concrete Product : Concrete classes that implement or extends from Product
Creator : The class or Interface definde a facetoryMethod method that returns Product
Concrete creator : Concrete class implmenting the method facetoryMethod to create the Concrete Product

Example

Product class initialztation


interface Logger {
    public function log(string $message): void;
}

class FileLogger implements Logger {
    public function log(string $message): void {
        echo "Logging to a file: $message";
    }
}

class DatabaseLogger implements Logger {
    public function log(string $message): void {
        echo "Logging to a database: $message";
    }
}

Creator and Concrete Creator


abstract class LoggerFactory {
    // Phương thức factory method
    abstract public function createLogger(): Logger;

    public function log(string $message): void {
        $logger = $this->createLogger();
        $logger->log($message);
    }
}

class FileLoggerFactory extends LoggerFactory {
    public function createLogger(): Logger {
        return new FileLogger();
    }
}

class DatabaseLoggerFactory extends LoggerFactory {
    public function createLogger(): Logger {
        return new DatabaseLogger();
    }
}

Ussing Facetory Method

// Tạo logger dạng File
$fileLoggerFactory = new FileLoggerFactory();
$fileLoggerFactory->log("This is a file log message.");

// Tạo logger dạng Database
$databaseLoggerFactory = new DatabaseLoggerFactory();
$databaseLoggerFactory->log("This is a database log message.");

Advantages of Factory Method

Scalable : create a new product, only need add product class and creator class respectively
Reuse : same business logic, but different objects can be created without modifying the main source code.
Separation of responsibilities : creator is responsible for object initialization , initialization logic is not part of business logic

Disadvantages

the code more complicated, because it requires additional creator class and Concrete Product classes
Ability extends ,requires the initial design to be accurate

Example 2: CRUD (User and Role) in PHP

Setup interface


interface CrudInterface {
    public function create(array $data): void;
    public function read(int $id): ?array;
    public function update(int $id, array $data): void;
    public function delete(int $id): void;
}

Product (User Role)

class User implements CrudInterface {
    private $users = []; // Mô phỏng cơ sở dữ liệu

    public function create(array $data): void {
        $this->users[$data['id']] = $data;
        echo "User created: " . json_encode($data) . PHP_EOL;
    }

    public function read(int $id): ?array {
        return $this->users[$id] ?? null;
    }

    public function update(int $id, array $data): void {
        if (isset($this->users[$id])) {
            $this->users[$id] = array_merge($this->users[$id], $data);
            echo "User updated: " . json_encode($this->users[$id]) . PHP_EOL;
        } else {
            echo "User not found." . PHP_EOL;
        }
    }

    public function delete(int $id): void {
        unset($this->users[$id]);
        echo "User deleted: $id" . PHP_EOL;
    }
}

class Role implements CrudInterface {
    private $roles = []; // Mô phỏng cơ sở dữ liệu

    public function create(array $data): void {
        $this->roles[$data['id']] = $data;
        echo "Role created: " . json_encode($data) . PHP_EOL;
    }

    public function read(int $id): ?array {
        return $this->roles[$id] ?? null;
    }

    public function update(int $id, array $data): void {
        if (isset($this->roles[$id])) {
            $this->roles[$id] = array_merge($this->roles[$id], $data);
            echo "Role updated: " . json_encode($this->roles[$id]) . PHP_EOL;
        } else {
            echo "Role not found." . PHP_EOL;
        }
    }

    public function delete(int $id): void {
        unset($this->roles[$id]);
        echo "Role deleted: $id" . PHP_EOL;
    }
}

Create Factory class


abstract class CrudFactory {
    abstract public function createCrud(): CrudInterface;
}

class UserFactory extends CrudFactory {
    public function createCrud(): CrudInterface {
        return new User();
    }
}

class RoleFactory extends CrudFactory {
    public function createCrud(): CrudInterface {
        return new Role();
    }
}

Factory Method use CRUD

// Factory cho User
$userFactory = new UserFactory();
$userCrud = $userFactory->createCrud();

// Thực hiện các thao tác CRUD cho User
$userCrud->create(['id' => 1, 'name' => 'Hoa Dev', 'email' => 'hoadev@example.com']);
$userCrud->update(1, ['email' => 'hoadev.code@example.com']);
$userData = $userCrud->read(1);
echo "Read User: " . json_encode($userData) . PHP_EOL;
$userCrud->delete(1);

// Factory cho Role
$roleFactory = new RoleFactory();
$roleCrud = $roleFactory->createCrud();

// Thực hiện các thao tác CRUD cho Role
$roleCrud->create(['id' => 101, 'name' => 'Admin']);
$roleCrud->update(101, ['name' => 'Super Admin']);
$roleData = $roleCrud->read(101);
echo "Read Role: " . json_encode($roleData) . PHP_EOL;
$roleCrud->delete(101);

Results 👍

User created: {"id":1,"name":"Hoa Dev","email":"hoadev@example.com"}
User updated: {"id":1,"name":"Hoa Dev","email":"hoadev.code@example.com"}
Read User: {"id":1,"name":"Hoa Dev","email":"hoadev.code@example.com"}
User deleted: 1
Role created: {"id":101,"name":"Admin"}
Role updated: {"id":101,"name":"Super Admin"}
Read Role: {"id":101,"name":"Super Admin"}
Role deleted: 101