PHP - 最佳实践类中的全局数据库变量（OOP）[重复]

Question

This question already has an answer here:

• How can I use “Dependency Injection” in simple php functions, and should I bother? 5 answers

What is 'best practice' regarding accessing the database when you have multiple classes with methods that do queries?

Global $db variable:

$db = new mysqli('localhost', 'my_user', 'my_password', 'my_db');

class Item {
    private $id;

    function __construct($id) {
        $this->id = $id;
    }

    public function remove() {
        global $db;

        // queries and stuff.
    }
}

Or maybe, passing the $db to the constructor?

$db = new mysqli('localhost', 'my_user', 'my_password', 'my_db');

$item = new Item(5,$db);

class Item {
    private $id;
    protected $db;

    function __construct($id,$db) {
        $this->id = $id;
        $this->id = $db;
    }

    public function remove() {
        // queries and stuff.
    }
}

Or maybe another way is better than both of these?

</div>

Answer 1

For global objects which can potentially be used anywhere I personally prefer singleton classes:

class DBConnection {

     private static $instance = null;

     private $db;
     private function __construct() {
         $this->db = new mysqli('localhost', 'my_user', 'my_password', 'my_db');
     }

     public static function getDB() {
           if (self::$instance === null) { 
               self::$instance = new self();
           }
           return self::$instance->db;
     }    
}

This way you can just call: DBConnection::getDB() anywhere you need to, and this can also work with auto-loading.