Introduction to Design Patterns with PHP

Observer, decorator, factory method, composite… All these words refer to design patterns. Design patterns are general reusable solutions for solving common redundant problems in software architecture. Getting inspiration on some well known design patterns and implementing them in PHP will make your application code easier to understand, maintain and evolve. Based on practical code samples, this talk will focus on the most useful patterns in order to help you design better PHP applications.

1. Introduction to design patterns with PHP
2. Who are we? Hugo Hamon Julien Pauli
3. Object Oriented Programming in PHP...
4. Overview of OOP in PHP Objects and classes Abstract and final classes Interfaces Abstract & final Magic methods Garbage collector Object cloning Single inheritance SPL and more… Encapsulation Overloading (a bit...) Classes autoloading Type hinting Reflection Namespaces Traits
5. Object Oriented Design Best Practices
6. SOLID Principle Single Responsibility Principle Open Close Principle Liskov Substitution Principle Interface Segregation Principle Dependency Injection Principle
7. Single Responsability (SRP) « A class should have one, and only one, reason to change. » Keep your classes small and focused on small responsabilities.
8. class CsvDataImporter { public function import($file) { $records = array(); if (false !== $handle = fopen($file, 'r')) { while ($record = fgetcsv($handle)) { $records[] = $record; } } fclose($handle); try { $this->db->beginTransaction(); foreach ($records as $record) { $stmt = $this->db->prepare('INSERT INTO ...'); $stmt->execute($record); } $this->db->commit(); } catch (PDOException $e) { $this->db->rollback(); throw $e; } } }
9. class DataImporter { private $loader; private $table; function __construct(FileLoader $loader, TableGateway $table) { $this->loader = $loader; $this->table = $table; } public function import($file) { $records = $this->loader->load($file); return $this->table->insert($records); } }
10. Open Close (OCP) Software entities should be open to extension and close to modifications. « You should be able to extend a classe’s behavior, without modifying it. »
11. Open Close $loader = new CsvFileLoader(); $loader = new XmlFileLoader(); $loader = new JsonFileLoader(); $importer = new DataImporter($loader, ...); $importer->import('foo.csv|xml|json'); Using a different file loader is now very easy without changing the importer class.
12. Liskov Substitution A dependency of type T should be replaced by another subtype S of T without breaking the code. « Derived classes must be substitutable for their base classes. »
13. Liskov Substitution class TextFileLoader implements FileLoader { public function load($file) { // ... return [ ... ]; } } class CsvFileLoader extends TextFileLoader { public function load($file) { // ... return [ ... ]; } }
14. Interface Segregation (ISP) Interface segregation split larger interfaces into smaller ones so that clients will only know about the methods they need to work with. « Make fine grained interfaces that are client specific. »
15. Interface Segregation interface FileLoader { public function load($file); public function supports($type); } interface TableGateway { public function insert(array $records); }
16. Interface Segregation class DataImporter { public function __construct(FileLoader $loader, TableGateway $table) { // ... } public function import($file) { $ext = pathinfo($file, PATHINFO_EXTENSION); if (!$this->loader->supports($ext)) { throw new UnsupportedDataFile(); } $records = $this->loader->load($file); return $this->table->insert($records); } }
17. Dependency Injection (DIP) D.I is where components are given their dependencies through their constructors, methods, or directly into fields. « Depend on abstractions, not on concretions. »
18. DI – The Wrong Way class DataImporter { private $loader; private $table; public function __construct() { $this->loader = new CsvFileLoader(); $this->table = new TableGateway(); } }
19. DI – The Right Way class DataImporter { private $loader; private $table; function __construct(FileLoader $loader, TableGateway $table) { $this->loader = $loader; $this->table = $table; } }
20. DI – Injecting dependencies $importer = new DataImporter( new CsvFileLoader(), new TableGateway('data', new PDO(…)) ); $importer->import('foo1.csv'); $importer->import('foo2.csv'); $importer->import('foo3.csv');
21. Discovering Design Patterns
22. Definition In software design, a design pattern is an abstract generic solution to solve a particular redundant problem.
23. Communication
24. Unit testability
25. Design patterns families Abstract Factory Builder Factory Method Lazy Initialization Prototype Singleton Adapter Bridge Composite Decorator Facade Flyweight Proxy Chain of Responsability Command Interpreter Iterator Mediator Memento Observer State Strategy Template Method Visitor Creational Structural Behavioral
26. Design Patterns in Practice with PHP
27. Disclaimer Patterns are not the holy grail!
28. The Context A web store wants to sell hard and digital products. Shipment fees are calculated based on the product caracteristics (volume, mass, type…) Products are shipped to customers.
29. Composite http://www.flickr.com/photos/xtinalamb/59989462
30. Composite Composite lets clients treat individual objects and compositions of objects uniformly.
32. Common implementations 2. Treating XML nodes. 1. Representing categories trees. 3. Dealing with embedded forms.
33. input[type=text] textarea input[type=text] input[type=file] Form Form
34. Concrete Example My web store must be able to sell single items or grouped items.
35. Product! getPrice()! HardProduct! getPrice()! Bundle! add(Product $product)! getPrice()! getMass()! getVolume()!
36. abstract class Product { protected $name; protected $price; public function __construct($name, Money $price) { $this->name = $name; $this->price = $price; } abstract public function getMass(); abstract public function getVolume(); // ... a bunch of getters }
37. class HardProduct extends Product { // ... private $mass; private $volume; public function setPhysics(Mass $mass, Volume $volume) { $this->mass = $mass; $this->volume = $volume; } public function getMass() { return $this->mass; } public function getVolume() { return $this->volume; } }
38. class DigitalProduct extends Product { public function getMass() { return new Mass(0); } public function getVolume() { return new Volume(0); } }
39. class Bundle extends Product { protected $products; public function __construct($name) { $this->name = $name; } public function setPrice(Money $price) { $this->price = $price; } public function add(ProductInterface $product) { $this->products[] = $product; } }
40. class Bundle extends Product { public function getMass() { $mass = new Mass(0); foreach ($this->products as $product) { $mass = $mass->add($product->getMass()); } return $mass; } public function getVolume() { $volume = new Volume(0); foreach ($this->products as $product) { $volume = $volume->add($product->getVolume()); } return $volume; } }
41. class Bundle extends Product { public function getPrice() { if ($this->price) { return $this->price; } $price = $this->products[0]->getPrice(); for ($i = 1; $i < count($this->products); $i++) { $product = $this->products[$i]; $price = $price->add($product->getPrice()); } return $price; } }
42. $b1 = new Bundle('C'); $b1->setPrice(new Money(39)); $b1->addProduct(new HardProduct('A', new Money(29))); $b1->addProduct(new DigitalProduct('B', new Money(20))); echo $b1->getPrice(); // 39 EUR $b2 = new Bundle('D'); $b2->addProduct(new HardProduct('C', new Money(12))); echo $b2->getPrice(); // 12 EUR Usage: creating products
43. $b1 = new Bundle('C'); $b1->setPrice(new Money(39)); $b1->addProduct(new HardProduct('A', new Money(29))); $b1->addProduct(new DigitalProduct('B', new Money(20))); $b2 = new Bundle('D'); $b2->addProduct(new HardProduct('C', new Money(12))); $b3 = new Bundle('E'); $b3->addProduct($b1); $b3->addProduct($b2); echo $b3->getPrice(); // 39 + 12 = 51 EUR Usage: embedding bundles
44. http://soyou.wordpress.com/tag/poupees-russes/ Decorator
45. Adding responsibilities to objects without subclassing their classes. Goal
47. Common implementations 1.  Adding some caching capability to a web service client to avoid network calls if not needed. 2.  Adding some logging features to an object in a dev environment. For instance, a database connection.
48. Concrete Example We want to offer discounts on orders without breaking existing domain model. Discount strategies may vary depending on the context.
49. OrderInterface! Order! BasicRateDiscount! getAmount()! getAmount()! order! getAmount()! OrderDecorator!
50. class Order implements OrderInterface { private $products = array(); public function addProduct(Product $product) { $this->products[] = $product; } public function getAmount() { $total = new Money(0); foreach ($this->products as $product) { $total = $total->add($product->getPrice()); } return $total; } }
51. abstract class OrderDecorator implements OrderInterface { protected $order; public function __construct(OrderInterface $order) { $this->order = $order; } public function addProduct(Product $product) { return $this->order->addProduct($product); } }
52. class BasicValueDiscount extends OrderDecorator { private $discount; function __construct(OrderInterface $order, Money $discount) { parent::__construct($order); $this->discount = $discount; } function getAmount() { $amount = $this->order->getAmount(); return $amount->subtract($this->discount); } }
53. $order = new Order(...); $order->addProduct(new DigitalProduct('A', new Money(15))); $order->addProduct(new DigitalProduct('B', new Money(10))); // Substract 5 euros to the total $order1 = new BasicValueDiscount($order, new Money(5)); $order1->getAmount(); // 20 EUR // Substract 50% of the total $order2 = new BasicRateDiscount($order, 50); $order2->getAmount(); // 12.50 EUR // Combine discounts together $order3 = new BasicRateDiscount( new BasicValueDiscount($order, new Money(5)), 50 ); $order3->getAmount(); // 10 EUR Usage
54. Other discount strategies… + Minimum purchase amount required + Minimum ordered items required + Loyal clients only + Special first order discount + …
55. Pros and cons + Easy way to extend an object capabilities + No need to change the underlying code - Object construction becomes more complex - Difficulty to test the concrete object type
56. http://redmtncom.com/uploads/chess_pieces_photo.jpg Strategy
57. The strategy pattern encapsulates algorithms of the same nature into dedicated classes to make them interchangeable. Goal
58. Common implementations 1.  Switching to another storage engine to store session data. 2.  Comparing and sorting elements of an array. 3.  Sending emails with SMTP, Sendmail or the mail() function.
59. class Swift_Mailer { private $transport; public function __construct(Swift_Transport $transport) { $this->transport = $transport; } public function send(Swift_Message $message) { // do stuff… $this->transport->send($message); } } Swiftmailer example
60. class Swift_MailTransport extends Swift_Transport { public function send(Swift_Message $message) { // use php mail() function to send a message } } class Swift_SmtpTransport extends Swift_Transport { public function send(Swift_Message $message) { // use an SMTP connection to send a message } } class Swift_NullTransport extends Swift_Transport { public function send(Swift_Message $message) { // fake email sending } }
61. Concrete example We want to calculate the order shipment fees depending on the chosen delivery strategy. The customer can choose between 3 delivery strategies.
62. Concrete example (wrong!!!) class OrderService { function priceShippingCost(OrderInterface $order, $type) { switch ($type) { case 'warehouse-pickup': return new Money(0); case 'regular': return new Money(7); case 'express': return new Money(10); } } }
63. Encapsulating algorithms interface ShippingStrategy { function calculateShippingCost(OrderInterface $order); } class WarehousePickup implements ShippingStrategy { function priceShippingCost(OrderInterface $order) { return new Money(0); } }
64. Encapsulating algorithms class RegularShipping implements ShippingStrategy { function priceShippingCost(OrderInterface $order) { if ($order->getAmount() > 100) { return new Money(0); } if (count($order->getProduct()) > 3) { return new Money(12); } return new Money(7); } }
65. Encapsulating algorithms class ExpressShipping implements ShippingStrategy { function priceShippingCost(OrderInterface $order) { if ($order->getWeight() < 5) { return new Money(6); } if ($order->getWeight() >= 5 && $order->getWeight() < 10) { return new Money(9); } return new Money(15); } }
66. class OrderService { public function priceShippingCost( OrderInterface $order, ShippingStrategy $shipping ) { // ... do stuff $fare = $shipping->priceShippingCost($order); $order->getAmount()->add($fare); // ... do stuff } } Strategy can be given as an argument of the client’s method.
67. class OrderService { private $shippingStrategy; public function __construct(ShippingStrategy $shipping) { $this->shippingStrategy = $shipping; } public function priceShippingCost(OrderInterface $order, $delivery) { // ... do stuff $fare = $this->shippingStrategy->priceShippingCost($order); $order->getAmount()->add($fare); // ... do stuff } } Or it can be injected in the constructor method of the client.
68. http://www.flickr.com/photos/jerryms/6704324441 Factory Method
69. Goal Define an interface for creating an object, but let subclasses decide which class to instantiate.
70. Factory Method lets a class defer instantiation to subclasses.
72. Concrete example We want to encapsulate the way we create hard products, digital products and bundles. The goal is to keep instantiation processes in one single place.
73. ProductFactory + createProduct($name) + newProduct($name, $price) Product HardProduct HardProductFactory + createProduct($name)
74. abstract class ProductFactory { public function __construct(ReferenceGenerator $generator) { $this->refGenerator = $generator; } abstract protected function createProduct($name, $price, $mass = null, $volume = null); public function newProduct($name, $price, $mass = null, $volume = null) { $price = new Price($price, new Currency('EUR')); $product = $this->createProduct($name, $price, $mass, $volume); $product->setReference($this->refGenerator->generate($product)); return $product; } } Usage
75. class HardProductFactory extends ProductFactory { protected function createProduct( $name, Price $price, Mass $mass = null, Volume $volume = null ) { $product = new HardProduct($name, $price); $product->setPhysics($mass, $volume); return $product; } }
76. class DigitalProductFactory extends ProductFactory { protected function createProduct( $name, Price $price, Mass $mass = null, Volume $volume = null ) { return new DigitalProduct($name, $price); } }
77. class BundleFactory extends ProductFactory { protected function createProduct( $name, Price $price, Mass $mass = null, Volume $volume = null ) { return new Bundle($name, $price); } }
78. $generator = new ReferenceGenerator(); $factory = new HardProductFactory($generator); $product = $factory->newProduct('A', 50, 4, 10); $factory = new DigitalProductFactory($generator); $product = $factory->newProduct('B', 25); $factory = new BundleFactory($generator); $bundle = $factory->newProduct('C', 99); Usage
79. Observer
80. Goal A subject, the observable, emits a signal to a list of modules known as observers.
81. class Customer { public function pay(Order $order, Money $amount) { $order->setPaid(); if ($this->logger) { $this->logger->log('New order...'); } $mail = new Email(); $mail->recipient = $this->customer->getEmail(); $mail->subject = 'Your order!'; $mail->message = 'Thanks for ordering...'; $this->mailer->send($mail); $mail = new Email(); $mail->recipient = 'sales@acme.com'; $mail->subject = 'New order to ship!'; $mail->message = '...'; $this->mailer->send($mail); } }
83. interface ObserverInterface { function notify(ObservableInterface $subject); } interface ObservableInterface { function attach(ObserverInterface $observer); function notifyObservers(); }
84. class LoggerHandler implements ObserverInterface { public $logger; public function notify(ObservableInterface $subject) { $order = $subject->getLastOrder(); $reference = $order->getReference(); $this->logger->log('New order #'. $reference); } }
85. class CustomerNotifier implements ObserverInterface { public $mailer; public function notify(ObservableInterface $subject) { $mail = new Email(); $mail->recipient = $subject->getEmail(); $mail->subject = 'Your order!'; $mail->message = 'Thanks for ordering...'; $this->mailer->send($mail); } }
86. class SalesNotifier implements ObserverInterface { public $mailer; public function notify(ObservableInterface $subject) { $mail = new Email(); $mail->recipient = 'sales@acme.com'; $mail->subject = 'New order to ship!'; $mail->message = '...'; $this->mailer->send($mail); } }
87. class Customer implements ObservableInterface { // ... private $observers; public function attach(ObserverInterface $observer) { $this->observers[] = $observer; } public function notifyObservers() { foreach ($this->observers as $observer) { $observer->notify($this); } } }
88. class Customer implements ObservableInterface { public function pay(Order $order) { $order->setPaid(); $this->notifyObservers(); } }
89. $client = new Customer(); $client->attach(new LoggerNotifier($logger)); $client->attach(new CustomerNotifier($mailer)); $client->attach(new SalesNotifier($mailer)); $order = new Order(); $client->pay($order, new Money(150));
90. Conclusion…
91. Good readings