//Dependency injection is a big word for "I have some more parameters in my constructor".
//It's what you did before the awfull Singleton wave when you did not like globals :
class User {
private $_db;
function __construct($db) {
$this->_db = $db;
}
}
$db = new Db();
$user = new User($db);
//Now, the trick is to use a single class to manage your dependencies, something like that :
class DependencyContainer
{
private _instances = array();
private _params = array();
public function __construct($params)
{
$this->_params = $params;
}
public function getDb()
{
if (empty($this->_instances['db'])
|| !is_a($this->_instances['db'], 'PDO')
) {
$this->_instances['db'] = new PDO(
$this->_params['dsn'],
$this->params['dbUser'],
$this->params['dbPwd']
);
}
return $this->_instances['db'];
}
}
class User
{
private $_db;
public function __construct(DependencyContainer $di)
{
$this->_db = $di->getDb();
}
}
$dependencies = new DependencyContainer($someParams);
$user = new User($dependencies);
/*
You must think you just another class and more complexity. But, your user class may need something to log messages like lot of other classes. Just add a getMessageHandler function to your dependency container, and some $this->_messages = $di->getMessageHandler() to your user class. Nothing to change in the rest of your code.
*/
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