public function __construct(User $user)
 {
     $this->id = $user->getId();
     $this->username = $user->getUsername();
 }
 private static function update(User $model)
 {
     $db = Db::getInstance(\ConferenceScheduler\Configs\DatabaseConfig::DB_INSTANCE);
     $query = "UPDATE users SET username= :username, password= :password, email= :email, telephone= :telephone WHERE id = :id";
     $result = $db->prepare($query);
     $result->execute([':id' => $model->getId(), ':username' => $model->getUsername(), ':password' => $model->getPassword(), ':email' => $model->getEmail(), ':telephone' => $model->getTelephone()]);
 }