Practical Design PHPatterns

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Practical Design PHPatterns Hugo Hamon – PHPBenelux 2013 - Antwerp http://wwp.greenwichmeantime.com

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What are design patterns?

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Definition « In software design, a design pattern is an abstract generic solution to solve a particular redundant problem. »

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Patterns categories Creation Structure Behavior

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Want to learn?

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Disclaimer Patterns are not the holly grail!

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Today’s patterns o  Facade o  Adapter o  Template Method o  Strategy o  Decorator o  Composite o  Factory Method o  Observer

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Facade http://www.flickr.com/photos/br1dotcom/5930994659

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Wrapping a complicated system in order to provide a simplier interface to use it. Goal

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Parsing an Atom XML feed to extract some information. Practical Example

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$content = file_get_contents(__DIR__.'/feed.xml'); $xml = new SimpleXMLElement($content); $title = (string) $xml->title; $entries = array(); $entry = array(); foreach ($this->xml->entry as $entry) { $entry['title'] = (string) $entry->title; $entry['summary'] = (string) $entry->summary; $entry['id'] = (string) $entry->id; if (isset($entry->author)) { // parse node $author = ...; $entry['author'] = $author; } $entries[] = $entry; $entry = array(); }

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Encapsulating the complex xml parsing logic into a facade object. Solution

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class FeedReader { public function getTitle() { [complex xml parsing logic here] } public function getEntries() { [complex xml parsing logic here] } }

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public function getEntries() { if (null === $this->xml) { $this->loadXml(); } $entries = array(); $entry = array(); foreach ($this->xml->entry as $entry) { $entry['title'] = (string) $entry->title; $entry['summary'] = (string) $entry->summary; $entry['id'] = (string) $entry->id; if ($author = $this->getAuthor($entry)) { $entry['author'] = $author; } $entries[] = $entry; $entry = array(); } return $entries; }

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$facade = new FeedReader('feed.xml'); $title = $facade->getTitle(); $entries = $facade->getEntries(); foreach ($entries as $entry) { echo $entry['title'],"\n"; if (isset($entry['author'])) { echo $entry['author']['name']; } }

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Adapter

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Providing a unique API to objects that don’t share the same API. Goal

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Fetching weather forecasts with two different weather providers, which don’t have the same API. Practical Example

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A weather client object relies on the famous WahooWeather web service to collect daily forecasts for a city.

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class WeatherService { private $api; public function __construct(WahooWeatherApi $api) { $this->api = $api; } public function getForecasts($city, $date) { return $this->api->getCityForecasts($city, $date); } }

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But a new competitor, BoogleWeather, now comes with a much more powerful API to get daily forecasts for a city.

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We want the weather service Client supports both weather providers although they don’t share the same API at all…

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$api = new WahooWeatherApi(); $result = $api->getCityForecasts('Paris', '2013-02-25'); $result = array( 'city' => 'Paris', 'country' => 'France', 'date' => '2013-02-25', 'conditions' => 'snowy', 'temperature' => '-6', 'unit' => 'C', );

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$weather = new BoogleWeather(); $weather->city = 'Paris'; $weather->date = '02/25/2013'; $json = $weather->getForecasts(); $json = '{ "location": "Paris, France", "temp": "21.2", "conditions": "snowy", "date": "02\/05\/2013” }';

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WahooWeatherApi BoogleWeather Date in YYYY-mm-dd format Date in mm/dd/YYYY format City is passed to the method City is set in a public property Method is getCityForecasts() Method is getForecasts() Returns an array Returns a JSON string APIs differences

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Designing an Adapter helps to provide a single public API to support the two heterogeneous Adaptees.

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abstract class WeatherProviderAdapter { protected $date; public function setDate($date) { $this->date = new DateTime($date); } abstract public function getForecasts($city); }

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class WahooProviderAdapter extends WeatherProviderAdapter { private $api; public function __construct(WahooWeatherApi $api) { $this->api = $api; } public function getForecasts($city) { $date = $this->date->format('Y-m-d'); return $this->api->getCityForecasts($city, $date); } }

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class BoogleProviderAdapter extends WeatherProviderAdapter { private $api; public function __construct(BoogleWeather $api) { $this->api = $api; } public function getForecasts($city) { $this->api->date = $this->date->format('m/d/Y'); $this->api->city = $city; $json = $this->api->getWeather(); // Convert the JSON output to an array expected by the client return $this->normalize($json); } }

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class WeatherService { private $provider; public function __construct(WeatherProviderAdapter $provider) { $this->provider = $provider; } public function getForecasts($city, $date) { $this->provider->setDate($date); return $this->provider->getForecasts($city); } }

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// Adapter for the Wahoo weather service $adaptee = new WahooWeatherApi(); $adapter = new WahooProviderAdapter($adaptee); // Adapter for the Boogle weather service $adaptee = new BoogleWeather(); $adapter = new BoogleProviderAdapter($adaptee); // Client code that deals with the adapters $client = new WeatherService($adapter); $client->getForecasts('Paris', '2013-02-25');

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Template Method http://www.flickr.com/photos/jmgeorges/4849023808

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Let subclasses redefine certain steps of an algorithm without changing the algorithm’s structure. Goal

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Inserting or updating a record in a datastore like a relational or nosql database. Practical Example

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Mapper! RelationalMapper! NoSQLMapper! + save($data) [final]! # getPrimaryKey(array $data)! # insert(array $data)! # update($pk, array $data)! # getPrimaryKey(array $data)! # insert(array $data)! # update($pk, array $data)! # getPrimaryKey(array $data)! # insert(array $data)! # update($pk, array $data)!

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abstract class Mapper { /** * Inserts or updates a record in a datastore. * * @param array $data The data to insert or update * @return Boolean */ final public function save(array $data) { if ($pk = $this->getPrimaryKey($data)) { return $this->update($pk, $data); } return $this->insert($data); } abstract protected function getPrimaryKey(array $data); abstract protected function update($pk, array $data); abstract protected function insert(array $data); }

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class ArticleMapper extends Mapper { private $dbh; public function __construct(PDO $dbh) { $this->dbh = $dbh; } protected function getPrimaryKey(array $data) { return isset($data['id']) ? $data['id'] : null; } }

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class ArticleMapper extends Mapper { protected function insert(array $data) { $stmt = $this->dbh->prepare('INSERT INTO ... '); $stmt->bindValue(':title', $data['title'], PDO::PARAM_STR); $stmt->bindValue(':body', $data['body'], PDO::PARAM_STR); $stmt->execute(); return 1 === (int) $stmt->rowCount(); } protected function update($pk, array $data) { $stmt = $this->dbh->prepare('UPDATE ... WHERE id = :id '); $stmt->bindValue(':title', $data['title'], PDO::PARAM_STR); $stmt->bindValue(':body', $data['body'], PDO::PARAM_STR); $stmt->bindValue(':id', $pk, PDO::PARAM_INT); $stmt->execute(); return 1 === (int) $stmt->rowCount(); } }

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class LogMapper extends Mapper { private $mongo; public function __construct(MongoClient $mongo) { $this->mongo = $mongo; } protected function getPrimaryKey(array $data) { return isset($data['_id']) ? $data['_id'] : null; } }

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class LogMapper extends Mapper { protected function insert(array $data) { $data = $this->mongo->log->insert($data); return !empty($data['_id']); } protected function update($pk, array $data) { return $this->mongo->log->update($data); } }

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Strategy http://redmtncom.com/uploads/chess_pieces_photo.jpg

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The Strategy pattern encapsulates algorithms of the same nature into dedicated classes to make them interchangeable. Goal

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Sending emails with several transport layers like SMTP or the PHP mail function. Practical Example

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class Mailer { public function send(Message $message) { $to = $message->getRecipients(); $subject = $message->getSubject(); $body = $message->getBody(); $headers = $message->getHeaders(); if (!mail($to, $subject, $body, $headers)) { throw new RuntimeException('...'); } } }

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What if we want to use an SMTP transport to send the email? Practical Example

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class Mailer { private $transport; public function __construct($transport) { $this->transport = $transport; } public function send(Message $message) { $to = $message->getRecipients(); // ... if ('smtp' === $this->transport) { // ... use SMTP transport } else { // ... use mail function } } }

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interface MailTransportInterface { function send(Message $message); } Clean strategy interface

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class MailTransport implements MailTransportInterface { public function send(Message $message) { $to = $message->getRecipients(); $subject = $message->getSubject(); $body = $message->getBody(); $headers = $message->getHeaders(); if (!mail($to, $subject, $body, $headers)) { throw new MailTransportException('...'); } } }

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class SmtpTransport implements MailTransportInterface { public function send(Message $message) { // ... use an SMTP server } } class NullTransport implements MailTransportInterface { public function send(Message $message) { // do nothing } }

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class Mailer { private $transport; public function __construct(MailTransportInterface $transport) { $this->transport = $transport; } public function send(Message $message) { try { $this->transport->send($message); } catch (MailTransportException $e) { // ... handle error } } } Abstraction

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$transport = new MailTransport(); $transport = new NullTransport(); $transport = new SendmailTransport(); $transport = new SmtpTransport('localhost', 'user'); $message = new Message(); $message->setTo('[email protected]'); $message->setFrom('[email protected]'); $message->setSubject('Example'); $message->setBody('Some body'); $mailer = new Mailer($transport); $mailer->send($message);

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Decorator http://soyou.wordpress.com/tag/poupees-russes/

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Adding responsibilities to objects without subclassing their classes. Goal

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Adding new responsabilities to a database connection object. Practical Example

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class Connection implements ConnectionInterface { private $dbh; private $logger; private $queryCount; public function __construct(PDO $dbh, Logger $logger = null) { $this->logger = $logger; $this->dbh = $dbh; } public function getQueryCount() { return $this->queryCount; } }

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class Connection implements ConnectionInterface { // ... public function query($query) { if (null !== $this->logger) { $this->logger->log('Query: '.$query); $this->queryCount++; } return $this->dbh->query($query); } }

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Testing if the logger is set in production will add a small overhead for each executed SQL query.

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What if we want to extend the Connection class without introducing a dependency with the logger?

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Connection! ConnectionDecorator! MasterSlaveConnection! ProfiledConnection! query($query)! query($query)! query($query)! connection! query($query)!

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abstract class ConnectionDecorator implements ConnectionInterface { protected $connection; public function __construct(ConnectionInterface $connection) { $this->connection = $connection; } public function query($query) { return $this->connection->query($query); } }

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class ProfiledConnection extends ConnectionDecorator { private $logger; private $queryCount; function __construct(Connection $conn, Logger $logger) { parent::__construct($conn); $this->logger = $logger; $this->queryCount = 0; } public function getQueryCount() { return $this->queryCount; } }

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class ProfiledConnection extends ConnectionDecorator { public function query($query) { $this->logger->log('Query: '.$query); $this->queryCount++; return parent::query($query); } }

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$logger = new Logger(__DIR__.'/logs/demo.log'); $dbh = new PDO('mysql:...', 'root'); $conn = new Connection($dbh); $conn = new ProfiledConnection($conn, $logger); $conn->query("SET NAMES 'UTF8'"); $conn->query('SELECT * FROM users'); echo 'Queries count:'; echo $conn->getQueryCount(); // 2

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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

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Composite http://www.flickr.com/photos/xtinalamb/59989462

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Goal Composite lets clients treat individual objects and compositions of objects uniformly.

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Representing an HTML form as a list of Field objects. Practical Example

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input[type=text] textarea input[type=text] input[type=file] Form Form

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A Form is a collection of Field. A Field can also be a Form when it embeds several fields.

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Field! setData($data)! Input! setData($name)! Form! setData($name)! add($name, Field $field)! remove($name)! getFields()!

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$form = new Form('product'); $form->add('name', new Input('text')); $form->add('description', new Textarea()); $picture = new Form(); $picture->add('caption', new Input('text')); $picture->add('image', new Input('file')); $form->add('photo', $picture); $data = array( 'name' => 'Apple Macbook Air 11', 'description' => 'The finest laptop', 'photo' => array( 'caption' => 'The new Macbook Air.', ), ); $form->setData($data);

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abstract class Field { protected $name; protected $data; public function setName($name) { $this->name = $name; } public function setData($data) { $this->data = $data; } public function getData() { return $this->data; } }

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class Input extends Field { private $type; public function __construct($type) { $this->type = $type; } public function setData($data) { if ('file' !== $this->type) { parent::setData($data); } } }

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class Form extends Field { private $fields = array(); public function add($name, Field $field) { $this->fields[$name] = $field; $field->setName($name); } }

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class Form extends Field { public function setData($data) { foreach ($this->fields as $name => $field) { if (isset($data[$name])) { $field->setData($data[$name]); } } } public function getData() { $data = array(); foreach ($this->fields as $name => $field) { $data[$name] = $field->getData(); } return $data; } }

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Factory Method http://www.flickr.com/photos/jerryms/6704324441

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Goal Define an interface for creating an object, but let subclasses decide which class to instantiate.

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Creating several kind of Document objects with a factory (images, pdf, text…) Practical Example

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abstract class DocumentFactory { static public function getDocument($type) { switch ($type) { case "image": return new Image(); case "pdf": return new Pdf(); case "video": return new Video(); default: throw new InvalidArgumentException(); } } }

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Goal Factory Method lets a class defer instantiation to subclasses.

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DocumentFactory + createDocument($name) + newDocument($name, $content) Document Image ImageFileFactory + createDocument($name)

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abstract class DocumentFactory { protected $directory; public function __construct($directory) { $this->directory = $directory; } abstract public function createDocument($name); public function newDocument($name, $content) { $document = $this->createDocument($name); $document->setDirectory($this->directory); $document->setContent($content); $document->save(); return $document; } }

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class TextFileFactory extends DocumentFactory { public function createDocument($name) { return new Document($name); } }

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class ImageFileFactory extends DocumentFactory { public function createDocument($name) { $image = new Image($name); $image->setWidth(90); $image->setHeight(120); return $image; } }

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$binary = $graphic->getBinaryContent(); $factory = new ImageFileFactory(__DIR__.'/images'); $image = $factory->newDocument('lolcat.jpg', $binary); $content = 'README CAREFULLY'; $factory = new TextFileFactory(__DIR__.'/files'); $file = $factory->newDocument('README.txt', $content);

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Observer

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Goal A subject, the observable, emits a signal to a list of modules known as observers.

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Decoupling the dependencies of a domain object. Practical Example

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class Order { public function confirm() { $this->status = 'confirmed'; $this->save(); if ($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 = '[email protected]'; $mail->subject = 'New order to ship!'; $mail->message = '...'; $this->mailer->send($mail); } }

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interface ObserverInterface { function notify(ObservableInterface $subject); } interface ObservableInterface { function attach(ObserverInterface $observer); function notify(); }

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class LoggerHandler implements ObserverInterface { public $logger; public function notify(ObservableInterface $subject) { $reference = $subject->getReference(); $this->logger->log('New order #'. $reference); } }

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class CustomerNotifier implements ObserverInterface { public $mailer; public function notify(ObservableInterface $subject) { $mail = new Email(); $mail->recipient = $subject->customer->getEmail(); $mail->subject = 'Your order!'; $mail->message = 'Thanks for ordering...'; $this->mailer->send($mail); } }

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class SalesNotifier implements ObserverInterface { public $mailer; public function notify(ObservableInterface $subject) { $mail = new Email(); $mail->recipient = '[email protected]'; $mail->subject = 'New order to ship!'; $mail->message = '...'; $this->mailer->send($mail); } }

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class Order implements ObservableInterface { // ... private $observers; public function attach(ObserverInterface $observer) { $this->observers[] = $observer; } public function notifyObservers() { foreach ($this->observers as $observer) { $observer->notify($this); } } }

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class Order implements ObservableInterface { public function confirm() { $this->status = 'confirmed'; $this->save(); $this->notifyObservers(); } }

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$order = new Order(); $order->attach(new LoggerNotifier($logger)); $order->attach(new CustomerNotifier($mailer)); $order->attach(new SalesNotifier($mailer)); $order->customer = $customer; $order->amount = 150; $order->confirm();