<?php
    class User {

    public function Connect()
    {
        $dsn = "mysql:host=localhost;dbname=auto;charset=utf8";
        $opt = array (
            PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC
        );
        $pdo = new PDO('mysql:host=localhost;dbname=auto', 'root', '');
        return $pdo;
    }

    public function XMLtoDb()
    {
        $pdo = $this->Connect();
        $xml = new SimpleXMLElement('<?xml version="1.0" encoding="UTF-8"?><users></users>');
        $stmt = $pdo->query('SELECT login, password, fio, email, adres FROM users');
        while($row = $stmt->fetch(PDO::FETCH_ASSOC)){
            $user = $xml->addChild('user');
                foreach ($row as $key => $value) {
                    $user->addChild($key, $value);
                }
            }
        echo $xml->asXML("result.xml");
    }

     public function DbtoXML()
    {
        $pdo = $this->Connect();
        $string = file_get_contents('result.xml');
        $xml = new SimpleXMLElement($string);
        foreach($xml->user as $item){
            $login = $item->login;
            $password = $item->password;
            $fio = $item->fio;
            $email = $item->email;
            $adres = $item->adres;
            $stm = $pdo->prepare("INSERT INTO users (login, password, fio, email, adres) VALUES (? ,? ,?, ?, ?)");
            $stm->bindParam(1, $login);
            $stm->bindParam(2, $password);
            $stm->bindParam(3, $fio);
            $stm->bindParam(4, $email);
            $stm->bindParam(5, $adres);
            $users=$stm->execute();
        }
    }
}
    $object = new User;
    $object->XMLtoDb();
    $object->DbtoXML();
?>