Dependency Injection Reinventing how you manage PHP classes 

DI? What is DI? 

Dependency Injection means giving an object its instance variables. Really. That's it. - James Shore The Really Short Version 

Why This Kolaveri DI? 

Why This Kolaveri DI? CHANGE 

Why DI? • Maintainable • Extendible • Flexible • Configurable • Testable • Reusable • Interoperable 

A Real Life Example 

“Dependency Injection” is a 25-dollar term for a 5-cent concept. Don’t Panic! 

A PHP Example 

class MySqlDB { private $_link; public function __construct($host, $username, $password, $database) { $this->_link = mysql_connect($host, $username, $password); mysql_select_db($database); } public function insert($data, $table) { array_map('mysql_real_escape_string', $data); $query = 'INSERT INTO `' . $table . '` (`' . implode('`,`', array_keys($data)) . '`)' . 'VALUES ("' . implode('","', $data) . '" )'; return mysql_query($query, $this->_link); } // ... } 

define('MYSQL_HOST', 'localhost'); define('MYSQL_USER', 'root'); define('MYSQL_PASS', ''); define('MYSQL_DB', 'test'); class User { private $_db; private $_info = array(); public function __construct() { $this->_db = new MySqlDB(MYSQL_HOST, MYSQL_USER, MYSQL_PASS, MYSQL_DB); } public function register($name, $email, $age, $sex) { $this->_info = compact('name', 'email', 'age', 'sex'); $this->_db->insert($this->_info, 'users'); } // ... } $user = new User(); $user->register('Tasneem', '[email protected]', 18, 'female'); 

// You can hardcode it public function __construct() { $this->_db = new MySqlDB('localhost', 'root', '', 'test'); } // You can configure it with an array public function __construct($config) { $this->_db = new MySqlDB($config['host'], $config['user'], $config['pass'], $config['db']); } // And, What we saw earlier public function __construct() { $this->_db = new MySqlDB(MYSQL_HOST, MYSQL_USER, MYSQL_PASS, MYSQL_DB); } Options 

What if I want to use a different database like MongoDB or SQLite 

Hey wait, I can improve it! 

class User { protected $_db; protected $_info = array(); public function __construct() { $registry = RegistrySingleton::getInstance(); $this->_db = $registry->database; } public function register($name, $email, $age, $sex) { $this->_info = compact('name', 'email', 'age', 'sex'); $this->_db->insert($this->info, 'users'); } // ... } $user = new User(); $user->register('Tasneem', '[email protected]', 18, 'female'); 

Smart Huh??? 

So, now User depends on Registry 

Let’s do it with DI 

class User { protected $_db; protected $_info = array(); public function __construct($database) { $this->_db = $database; } public function register($name, $email, $age, $sex) { $this->_info = compact('name', 'email', 'age', 'sex'); $this->_db->insert($this->_info, 'users'); } // ... } $mysql = new MySqlDB('localhost', 'root', '', 'test'); $user = new User($mysql); $user->register('Tasneem', '[email protected]', 18, 'female'); 

But there are still rooms for improvement 

Interface 

Ever heard of Type Hinting 

public function test(OtherClass $otherClass) { } public function testInterface(Interface $interface) { } public function testArray(array $inputArray) { } Type Hinting Since PHP 5.1 

interface Database { public function insert(array $data, $table); } class User { protected $_db; protected $_info = array(); public function __construct(Database $database) { $this->_db = $database; } public function register($name, $email, $age, $sex) { $this->_info = compact('name', 'email', 'age', 'sex'); $this->_db->insert($this->_info, 'users'); } // ... } $mysql = new MySqlDB('localhost', 'root', '', 'test'); $user = new User($mysql); $user->register('Tasneem', '[email protected]', 18, 'female'); 

class MySqlDB implements Database { protected $_link; public function __construct($host, $username, $password, $database) { $this->_link = mysql_connect($host, $username, $password); mysql_select_db($database); } public function insert(array $data, $table) { array_map('mysql_real_escape_string', $data); $query = 'INSERT INTO `' . $table . '` (`' . implode('`,`', array_keys($data)) . '`)' . 'VALUES ("' . implode('","', $data) . '" )'; return mysql_query($query, $this->_link); } // ... } MySQL 

class MongoDB implements Database { // ... public function insert(array $data, $table) { // Save the passed array using MongoDB } // ... } $mongoDb = new MongoDB('localhost', 'root', '', 'test'); $user = new User($mongoDb); $user->register('Tasneem', '[email protected]', 18, 'female'); MongoDB 

class SQLiteDB implements Database { // ... public function insert(array $data, $table) { // Save the passed array using SQLite } // ... } $sqlite = new SQLiteDB('app.db', 'test'); $user = new User($sqlite); $user->register('Tasneem', '[email protected]', 18, 'female'); SQLite 

class TestDB implements Database { protected $_data = array(); public function insert(array $data, $table) { $this->_data[$table] = $data; } public function get($table) { return $this->_data[$table]; } } $fakeDb = new TestDB(); $user = new User($fakeDb); $user->register('Tasneem', '[email protected]', 18, 'female'); print_r($fakeDb->get('users')); TestDB 

DI Container 

class Container { protected $s=array(); function __set($k, $c) { $this->s[$k]=$c; } function __get($k) { return $this->s[$k]($this); } } Twittee A DI Container in a Tweet using the power of PHP 5.3 

$c = new Container(); $c->mysql = function ($c) { return new MySqlDB('localhost', 'root', '', 'test'); } $c->user = function ($c) { $db = $c->mysql; return new User($db); } // When you need a user $user = $c->user; // Instead of $user = new User(); Container 

http://components.symfony-project.org/dependency-injection/ http://pimple.sensiolabs.org/ http://twittee.org/ More... 

Question? 

@rifat [email protected] http://VistaArc.com/ http://OmicronLab.com/ Thank You