Nette Dependency Injection

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.

Class Nette\DI\Container is a flexible implementation of the universal DI container. It ensures automatically, that instance of services are created only once.

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.

class MyContainer extends Nette\DI\Container
{

	protected function createServiceConnection()
	{
		return new Nette\Database\Connection(
			$this->parameters['dsn'],
			$this->parameters['user'],
			$this->parameters['password']
		);
	}

	protected function createServiceArticle()
	{
		return new Article($this->connection);
	}

}

Now we create an instance of the container and pass parameters:

$container = new MyContainer(array(
	'dsn' => 'mysql:',
	'user' => 'root',
	'password' => '***',
));

We get the service by calling the getService method or by a shortcut:

$article = $container->getService('article');

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:

class MyContainer extends Nette\DI\Container
{

	function createServiceConnection()
	{
		return new Nette\Database\Connection(
			$this->parameters['dsn'],
			$this->parameters['user'],
			$this->parameters['password']
		);
	}

	function createArticle()
	{
		return new Article($this->connection);
	}

}

$container = new MyContainer(...);

$article = $container->createArticle();

From the call of $container->createArticle() is evident, that a new object is always created. It is then a programmer's convention.