public static function createRandomAlphaNumeric($length = 8)
    {
        $chars  = array("abcdefghijklmnpqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ", "123456789");
        $count  = array((strlen($chars[0]) - 1), (strlen($chars[1]) - 1));
        $prefix = "";
        for ($i = 0; $i < $length; $i++) {
            $type = mt_rand(0, 1);
            $prefix .= substr($chars[$type], mt_rand(0, $count[$type]), 1);
        }
        return self::create($prefix);
    }