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‎readme.md‎

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Nette Dependency Injection
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==========================
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Nette Dependency Injection (DI)
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===============================
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[![Downloads this Month](https://img.shields.io/packagist/dm/nette/di.svg)](https://packagist.org/packages/nette/di)
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[![Build Status](https://travis-ci.org/nette/di.svg?branch=master)](https://travis-ci.org/nette/di)
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Purpose of the Dependecy Injection (DI) is to free classes from the responsibility for obtaining objects that they need for its operation (these objects are called **services**). To pass them these services on their instantiation instead.
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Class `Nette\DI\Container` is a flexible implementation of the universal DI container. It ensures automatically, that instance of services are created only once.
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Nette DI is one of the most interesting part of framework. It is compiled DI container, extremely fast and easy to configure.
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Names of factory methods follow an uniform convention, they consist of the prefix `createService` + name of the service starting with first letter upper-cased. If they are not supposed to be accesible from outside, it is possible to lower their visibility to `protected`. Note that the container has already defined the field `$parameters` for user parameters.
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Let's have an application for sending newsletters. The code is maximally simplified and is available on the [GitHub](https://github.com/dg/di-example).
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We have the object representing email:
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```php
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class MyContainer extends Nette\DI\Container
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class Mail
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{
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public $subject;
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public $message;
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}
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```
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An object which can send emails:
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```php
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interface Mailer
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{
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function send(Mail $mail, $to);
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}
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```
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protected function createServiceConnection()
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A support for logging:
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```php
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interface Logger
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{
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function log($message);
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}
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```
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And finally, a class that provides sending newsletters:
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```php
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class NewsletterManager
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{
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private $mailer;
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private $logger;
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function __construct(Mailer $mailer, Logger $logger)
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{
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return new Nette\Database\Connection(
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$this->parameters['dsn'],
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$this->parameters['user'],
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$this->parameters['password']
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);
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$this->mailer = $mailer;
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$this->logger = $logger;
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}
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protected function createServiceArticle()
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function distribute(array $recipients)
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{
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return new Article($this->connection);
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$mail = new Mail;
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...
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foreach ($recipients as $recipient) {
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$this->mailer->send($mail, $recipient);
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}
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$this->logger->log(...);
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}
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}
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```
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The code respects Dependency Injection, ie. **each object uses only variables which we had passed into it.**
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Also, we have a ability to implement own `Logger` or `Mailer`, like this:
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```php
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class SendMailMailer implements Mailer
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{
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function send(Mail $mail, $to)
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{
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mail($to, $mail->subject, $mail->message);
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}
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}
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class FileLogger implements Logger
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{
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private $file;
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function __construct($file)
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{
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$this->file = $file;
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}
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function log($message)
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{
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file_put_contents($this->file, $message . "\n", FILE_APPEND);
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}
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}
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```
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**DI container is the supreme architect** which can create individual objects (in the terminology DI called services) and assemble and configure them exactly according to our needs.
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Container for our application might look like this:
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```php
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class Container
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{
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private $logger;
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private $mailer;
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function getLogger()
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{
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if (!$this->logger) {
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$this->logger = new FileLogger('log.txt');
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}
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return $this->logger;
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}
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function getMailer()
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{
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if (!$this->mailer) {
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$this->mailer = new SendMailMailer;
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}
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return $this->mailer;
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}
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function createNewsletterManager()
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{
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return new NewsletterManager($this->getMailer(), $this->getLogger());
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}
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}
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```
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Now we create an instance of the container and pass parameters:
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The implementation looks like this because:
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- the individual services are created only on demand (lazy loading)
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- doubly called `createNewsletterManager` will use the same logger and mailer instances
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Let's instantiate `Container`, let it create manager and we can start spamming users with newsletters :-)
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```php
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$container = new MyContainer(array(
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'dsn' => 'mysql:',
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'user' => 'root',
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'password' => '***',
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));
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$container = new Container;
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$manager = $container->createNewsletterManager();
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$manager->distribute(...);
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```
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Significant to Dependency Injection is that no class depends on the container. Thus it can be easily replaced with another one. For example with the container generated by Nette DI.
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Nette DI
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----------
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Nette DI is the generator of containers. We instruct it (usually) with configuration files. This is configuration that leads to generate nearly the same class as the class `Container` above:
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```neon
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services:
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- FileLogger( log.txt )
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- SendMailMailer
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- NewsletterManager
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```
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The big advantage is the shortness of configuration.
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Nette DI actually generates PHP code of container. Therefore it is extremely fast. Developer can see the code, so he knows exactly what it is doing. He can even trace it.
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Usage of Nette DI is very easy. In first, install it using Composer:
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```
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composer require nette/di
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```
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We get the service by calling the `getService` method or by a shortcut:
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Save the (above) configuration to the file `config.neon` and let's create a container:
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```php
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$article = $container->getService('article');
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$loader = new Nette\DI\ContainerLoader(__DIR__ . '/temp');
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$class = $loader->load('', function($compiler) {
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$compiler->loadConfig(__DIR__ . '/config.neon');
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});
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$container = new $class;
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```
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As have been said, all services are created in one container only once, but it would be more useful, if the container was creating always a new instance of `Article`. It could be achieved easily: Instead of the factory for the service `article` we'll create an ordinary method `createArticle`:
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and then use container to create object `NewsletterManager` and we can send e-mails:
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```php
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class MyContainer extends Nette\DI\Container
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$manager = $container->getByType('NewsletterManager');
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$manager->distribute(['[email protected]', ...]);
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```
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The container will be generated only once and the code is stored in cache (in directory `__DIR__ . '/temp'`). Therefore the loading of configuration file is placed in the closure in `$loader->load()`, so it is called only once.
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During development it is useful to activate auto-refresh mode which automatically regenerate the container when any class or configuration file is changed. Just in the constructor `ContainerLoader` append `TRUE` as the second argument:
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```php
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$loader = new Nette\DI\ContainerLoader(__DIR__ . '/temp', TRUE);
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```
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Services
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--------
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Services are registered in the DI container and their dependencies are automatically passed.
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```neon
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services:
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manager: NewsletterManager
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```
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All dependencies declared in the constructor of this service will be automatically passed. Constructor passing is the preferred way of dependency injection for services.
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If we want to pass dependencies by the setter, we can add the `setup` section to the service definition:
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```neon
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services:
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manager:
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factory: NewsletterManager
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setup:
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- setAnotherService
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```
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Class of the service:
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```php
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class NewsletterManager
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{
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private $anotherService;
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function createServiceConnection()
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public function setAnotherService(AnotherService $service)
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{
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return new Nette\Database\Connection(
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$this->parameters['dsn'],
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$this->parameters['user'],
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$this->parameters['password']
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);
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$this->anotherService = $service;
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}
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function createArticle()
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...
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```
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We can also add the `inject: yes` directive. This directive will enable automatic call of `inject*` methods and passing dependencies to public variables with `@inject` annotations:
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```neon
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services:
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foo:
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factory: FooClass
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inject: yes
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```
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Dependency `Service1` will be passed by calling the `inject*` method, dependency `Service2` will be assigned to the `$service2` variable:
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```php
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class FooClass
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{
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private $service1;
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// 1) inject* method:
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public function injectService1(Service1 $service)
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{
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return new Article($this->connection);
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$this->service1 = $service1;
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}
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// 2) Assign to the variable with the @inject annotation:
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/** @inject @var Service2 */
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public $service2;
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}
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```
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However, this method is not ideal, because the variable must be declared as public and there is no way how you can ensure that the passed object will be of the given type. We also lose the ability to handle the assigned dependency in our code and we violate the principles of encapsulation.
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Factories
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---------
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We can use factories generated from an interface. The interface must declare the returning type in the `@return` annotation of the method. Nette will generate a proper implementation of the interface.
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The interface must have exactly one method named `create`. Our factory interface could be declared in the following way:
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```php
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interface IBarFactory
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{
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/**
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* @return Bar
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*/
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public function create();
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}
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```
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The `create` method will instantiate an `Bar` with the following definition:
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```php
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class Bar
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{
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private $logger;
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public function __construct(Logger $logger)
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{
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$this->logger = $logger;
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}
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}
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```
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The factory will be registered in the `config.neon` file:
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```neon
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services:
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- IBarFactory
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```
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$container = new MyContainer(...);
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Nette will check if the declared service is an interface. If yes, it will also generate the corresponding implementation of the factory. The definition can be also written in a more verbose form:
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$article = $container->createArticle();
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```neon
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services:
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barFactory:
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implement: IBarFactory
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```
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From the call of `$container->createArticle()` is evident, that a new object is always created. It is then a programmer's convention.
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This full definition allows us to declare additional configuration of the object using the `arguments` and `setup` sections, similarly as for all other services.
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In our code, we only have to obtain the factory instance and call the `create` method:
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```php
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class Foo
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{
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private $barFactory;
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function __construct(IBarFactory $barFactory)
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{
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$this->barFactory = $barFactory;
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}
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function bar()
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{
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$bar = $this->BarFactory->create();
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}
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}
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```

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