효율적인 데이터베이스 운영을 위해 싱글톤 패턴으로 수업에서 PDO를 활용하는 방법은 무엇입니까?

<code class="php">class Core {
    private static $instance;
    public $dbh;

    private function __construct() {
        // Configuration and database connection initialization
    }

    public static function getInstance() {
        if (!isset(self::$instance)) {
            self::$instance = new self;
        }
        return self::$instance;
    }
}</code>

<code class="php">class Foo extends PDO {
    public $dbh;

    public function __construct() {
        $core = Core::getInstance();
        $this->dbh = $core->dbh;
    }

    public function bar() {
        $this->dbh->prepare('SELECT * FROM table');
        $this->dbh->execute();
    }
}</code>