Factory Method – Simple Factory, GoF, auto-generated factories in Magento 2

The new operator in production code is a warning sign. A class that directly instantiates other classes is tightly coupled to them – hard to test, hard to extend. Factory Method delegates the responsibility for object creation to dedicated classes. In Magento 2 factories are everywhere – and generated automatically.

The problem with the new keyword

<?php

class OrderProcessor
{
    public function process(array $data): void
    {
        // Tight coupling - cannot replace EmailNotifier in a test
        $notifier = new EmailNotifier();
        $logger   = new FileLogger('/var/log/orders.log');

        $notifier->send($data['email'], 'Order received');
        $logger->log('info', 'Order processed');
    }
}

Simple Factory – the entry point

<?php

interface NotifierInterface
{
    public function send(string $recipient, string $message): void;
}

class EmailNotifier implements NotifierInterface { /* ... */ }
class SmsNotifier   implements NotifierInterface { /* ... */ }
class SlackNotifier implements NotifierInterface { /* ... */ }

// Simple Factory - centralises creation logic
class NotifierFactory
{
    public function create(string $type): NotifierInterface
    {
        return match ($type) {
            'email' => new EmailNotifier(),
            'sms'   => new SmsNotifier(),
            'slack' => new SlackNotifier(),
            default => throw new \InvalidArgumentException("Unknown notifier: {$type}"),
        };
    }
}

$factory  = new NotifierFactory();
$notifier = $factory->create('email');
$notifier->send('jan@example.com', 'Order received');

Factory Method – the GoF pattern

<?php

abstract class OrderHandler
{
    // Factory method - subclasses implement this
    abstract protected function createNotifier(): NotifierInterface;

    // Business logic uses the notifier without knowing its type
    public function handle(array $orderData): void
    {
        $notifier = $this->createNotifier();
        $notifier->send($orderData['contact'], 'Order #' . $orderData['id'] . ' received');
    }
}

class EmailOrderHandler extends OrderHandler
{
    protected function createNotifier(): NotifierInterface
    {
        return new EmailNotifier();
    }
}

class SmsOrderHandler extends OrderHandler
{
    protected function createNotifier(): NotifierInterface
    {
        return new SmsNotifier();
    }
}

$handler = new EmailOrderHandler();
$handler->handle(['id' => 123, 'contact' => 'jan@example.com']);

Factory with DI – testable code

<?php

class NotifierFactory
{
    public function __construct(private array $notifiers = []) {}

    public function create(string $type): NotifierInterface
    {
        if (!isset($this->notifiers[$type])) {
            throw new \InvalidArgumentException("Notifier '{$type}' not registered");
        }
        return $this->notifiers[$type];
    }
}

class OrderProcessor
{
    public function __construct(private NotifierFactory $notifierFactory) {}

    public function process(array $orderData): void
    {
        $type     = $orderData['notification_type'] ?? 'email';
        $notifier = $this->notifierFactory->create($type);
        $notifier->send($orderData['contact'], 'Order received');
    }
}

<!-- Register notifiers via di.xml arguments -->
<type name="Vendor\Module\Model\NotifierFactory">
    <arguments>
        <argument name="notifiers" xsi:type="array">
            <item name="email" xsi:type="object">Vendor\Module\Model\EmailNotifier</item>
            <item name="sms"   xsi:type="object">Vendor\Module\Model\SmsNotifier</item>
            <item name="slack" xsi:type="object">Vendor\Module\Model\SlackNotifier</item>
        </argument>
    </arguments>
</type>

Adding a new notifier means a new class and one line in di.xml – zero changes to existing code.

Auto-generated factories in Magento 2

<?php

use Magento\Catalog\Model\ProductFactory;

class MyService
{
    public function __construct(
        private ProductFactory $productFactory
    ) {}

    public function createProduct(array $data): \Magento\Catalog\Model\Product
    {
        // create() always returns a new instance
        return $this->productFactory->create(['data' => $data]);
    }
}

Magento\Catalog\Model\ProductFactory does not exist in the Magento repository. It is generated by setup:di:compile into the generated/ directory based on the Product class. This is one of the most widely-used mechanisms in the Magento 2 ecosystem.

Summary

Factory Method separates object creation logic from business logic. Code becomes easier to test – inject a factory mock instead of real implementations. In Magento 2 auto-generated factories are the standard way to create new model instances, eliminating direct new in production code.