abstract class FileARModel
{
    private $dataFile;

    protected function __construct()
    {
        $this->dataFile = get_class($this) . '.txt';
    }

    protected function save()
    {
        file_put_contents($this->dataFile, serialize($this));
    }

    public static function loadById($id)
    {
        $allData = file($this->dataFile);
        foreach($allData as $line)
        {
            $user = unserialize($line);
            if($user->getId() == $id)
                return $user;
        }

        return null;
    }
}

class User extends FileARModel
{
    private $id = null;
    private $name;

    public function getId()
    {
        return $this->id;
    }

    public function getName()
    {
        return $this->id;
    }

    public function getName()
    {
        return $this->name;
    }

    public function setName($newName)
    {
        if($this->validateName($newName))
            $this->name = $newName;
        else
            throw new \Exception('Invalid name');
    }

    private function validateName($name)
    {
        return preg_match('#[a-z]*#iu', $name);
    }

    public function setId($id)
    {
        $id = intval($id);

        if($id <= 999999 || >= 999999999)
            throw new \Exception('invalid id');

        $this->id = $id;
    }
}