セッションがデータベースに保存されました

class SessionToDB
{
 private $_path = null;
 private $_name = null;
 private $_pdo = null;
 private $_ip = null;
 private $_maxLifeTime = 0;

 public function __construct(PDO $pdo)
 {
 session_set_save_handler(
 array(&$this, 'open'),
 array(&$this, 'close'),
 array(&$this, 'read'),
 array(&$this, 'write'),
 array(&$this, 'destroy'),
 array(&$this, 'gc')
 );

 $this->_pdo = $pdo;
 $this->_ip = !empty($_SERVER['REMOTE_ADDR']) ? $_SERVER['REMOTE_ADDR'] : null;
 $this->_maxLifeTime = ini_get('session.gc_maxlifetime');
 }

 public function open($path,$name)
 {
 return true;
 }

 public function close()
 {
 return true;
 }

 public function read($id)
 {
 $sql = 'SELECT * FROM session where PHPSESSID = ?';
 $stmt = $this- >_pdo->prepare($sql);
 $stmt->execute(array($id));

 if (!$result = $stmt->fetch(PDO::FETCH_ASSOC)) {
 return null;
 } elseif ($this->_ip != $result['client_ip']) {
 return null;
 } elseif ($result['update_time']+$this->_maxLifeTime < time( )){
 $this->destroy($id);
 return null;
 } else {
 return $result['data'];
 }
 }

 public function write($id,$data)
 {
 $sql = 'SELECT * FROM session where PHPSESSID = ?';
 $stmt = $this->_pdo->prepare($sql );
 $stmt->execute(array($id));

 if ($result = $stmt->fetch(PDO::FETCH_ASSOC)) {
 if ($result['data'] != $data) {
 $sql = 'UPDATE セッション SET update_time =? 、日付 = ? WHERE PHPSESSID = ?';

 $stmt = $this->pdo->prepare($sql);
 $stmt->execute(array(time(), $data, $id));
 }
 } else {
 if (!empty($data)) {
 $sql = 'INSERT INTO session (PHPSESSID, update_time, client_ip, data) VALUES (?,?,?,?)';
 $stmt = $this ->pdo->prepare($sql);
 $stmt->execute(array($id, time(), $this->_ip, $data));
 }
 }

 return true ;
 }

 public function destroy($id)
 {
 $sql = 'DELETE FROM session WHERE PHPSESSID = ?';
 $stmt = $this->_pdo->prepare($sql);
 $stmt ->execute(array($id));

 true を返します。
 }

 public function gc($maxLifeTime)
 {
 $sql = 'DELETE FROM session WHERE update_time < ?';
 $stmt = $this->pdo->prepare($sql);
 $stmt->execute(array(time() - $maxLifeTime));

 return true;
 }
}

try{
 $pdo = new PDO('mysql:host=localhost;dbname=rphp4zf', 'root','rickyfeng');
 $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION) ;

 新しい SessionToDB($pdo);
} catch(PDOException $e) {
 echo 'Error: '.$e->getMessage();
}