private function getShortUrlId($len = 7) { $chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890'; $charsLen = 62; $key = ''; for ($i = 0; $i < $len; $i++) { $key .= $chars[mt_rand() % $charsLen]; } return $key; }