public static function insert(User $user)
 {
     $query = "INSERT INTO users (mail, password, firstname, lastname, address, cp, city, phone, role)\n\t\t\tVALUES ('" . $user->getMail() . "','" . $user->getPassword() . "','" . $user->getFirstname() . "','" . $user->getLastname() . "','" . $user->getAddress() . "','" . $user->getCp() . "','" . $user->getCity() . "','" . $user->getPhone() . "','" . $user->getRole() . "')";
     if (DBOperation::exec($query)) {
         header('Location: index.php?controller=Front&method=home&success');
     } else {
         header('Location: index.php?controller=Front&method=signin&error');
     }
 }