PHP でデータベース対話用のクラスに PDO を効果的に統合するにはどうすればよいですか?

<code class="php">class Core
{
    private static $instance;
    private $dbh; // Database connection handle

    private function __construct()
    {
        // Initialize database connection using PDO
    }

    public static function getInstance()
    {
        if (!isset(self::$instance)) {
            self::$instance = new Core();
        }

        return self::$instance;
    }

    public function getPDO()
    {
        return $this->dbh;
    }
}</code>

<code class="php">class Foo
{
    public function bar()
    {
        $core = Core::getInstance();
        $dbh = $core->getPDO();

        $stmt = $dbh->prepare('SELECT * FROM table');
        $stmt->execute();
    }
}</code>