Problemer med klasse

Jeg har lavet følgende klasse til at oprette forbindelse til mysql:

<?php
class Mysql {
    private $connection;
    public static $instance;

    public function  __construct($host, $username, $password, $database, $newLink = false) {

    $this->connection = mysql_connect($host, $username, $password, $newLink);

        if (!$this->connection){
            throw new Exception("Could not connect to the server...");
        }

        if(!mysql_select_db($database, $this->connection)){
            throw new Exception("Could not connect to the database...");
        }
    }

    public static function instance(){

        if(!isset(Mysql::$instance)){
            Mysql::$instance = new Mysql(MYSQL_HOSTNAME, MYSQL_USERNAME, MYSQL_PASSWORD, MYSQL_DATABASE);
        }

        return Mysql::$instance;
    }

    public function selectDataObject($query){
        return mysql_fetch_object(mysql_query($query, $this->connection));
    }

    public function selectDataArray($query){
        return mysql_fetch_assoc(mysql_query($query, $this->connection));
    }

    public function  __destruct() {

        if(!mysql_close($this->connection)){
            throw new Exception("Could not close the connection to the server...");
        }

    }
}
?>

Nu vil jeg gerne udskrive det:
try {
$Database = Mysql::instance();
} catch (Exception $e) {
    echo 'Caught exception: ',  $e->getMessage(), "\n";
}

while($Data = $Database->selectDataObject("SELECT * FROM categories ORDER BY Name"))
{
echo $Data->ID;
}

Den finder også noget data fra databasen men udskriver bare det samme uendeligt, altså løkken stopper ikke.. :S