class User {

    private $userId;
    private $userDAO;

    public function __construct($dbh, $userId) {

        $this->userId = (int) $userId;
        //Create the UserDAO object
        $this->userDAO = new UserDAO($dbh, $this);

        //Get the up to date details of the user
        $userData = $this->userDAO->getUserData()

    }

}

class UserDAO {

    private $dbh;
    private $user;

    public function __construct($dbh, $user) {

        $this->dbh = $dbh;
        $this->user = $user;

    }

    public function getUserData() {

        $stmt = $this->dbh->prepare("SELECT username FROM " . USERS_TABLE . " WHERE userId = :userId LIMIT 1");
        $stmt->bindParam(':userId', $this->user->getUserId(), PDO::PARAM_INT);
        $stmt->execute();
        return $stmt->fetch(PDO::FETCH_ASSOC);

    }

}