Method isCurrencyValid

public static function isCurrencyValid($id)
{
    if ((int) $id > 0) {
        if (!array_key_exists((int) $id, self::$currencyvalid)) {
            $db = Factory::getDBO();
            $query = ' SELECT a.id FROM #__phocacart_currencies AS a' . ' WHERE a.id = ' . (int) $id . ' AND a.published = 1' . ' ORDER BY a.id';
            $db->setQuery($query);
            $c = $db->loadResult();
            if (isset($c) && (int) $c > 0) {
                self::$currencyvalid[$id] = true;
            } else {
                self::$currencyvalid[$id] = false;
            }
        }
        return self::$currencyvalid[$id];
    }
    return false;
}