PDO的事务处理

<?php
header('content-type:text/html;charset=utf-8');
include 'PdoClass.php';
$objPdo=new PdoClass();
//事务
try{
    $dsn = "mysql:host=localhost;dbname=xxx";
    $username = "root";
    $password = 'root';
    $pdo = new PDO($dsn, $username, $password,array(PDO::ATTR_AUTOCOMMIT=>0,PDO::ATTR_DEFAULT_FETCH_MODE=> PDO::FETCH_ASSOC,PDO::ATTR_CASE=>PDO::CASE_LOWER)) ;
    $pdo->exec('set names utf8');
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
}catch(PDOException $e){
    echo "connect fail：".$e->getMessage();
    exit;
}
try{
    $pdo->beginTransaction();
    $price = 500;
    $list=$objPdo->getAll('user');
    $goods = $objPdo->getAll('goods');
    //print_r($goods);die;
    $res=$list[0]['money'];
    $goods_count=$goods[0]['g_count'];
    if($res<500){
        throw new PDOException('从A帐号中扣出失败');
    }else if($goods_count==0){
        throw new PDOException('从商品表中扣出失败');
    }else {
        $sql = "update user set money=money-{$price} where u_id=1";
        $pdo->exec($sql);
        $sql1 = "update user set money=money+{$price} where u_id=2";
        $pdo->exec($sql1);
        $sql2 = "update goods set g_count=g_count-1 where g_id=1";
        $pdo->exec($sql2);
    }
    $pdo->commit();
} catch (PDOException $ex) {
    $pdo->rollBack();
    $title = isset($_POST['title'])?$_POST['title']:'';
    $list = $objPdo->getAll('user',$title);
    $goods = $objPdo->getAll('goods',$title);
    include 'form.html';
    echo $ex->getMessage();
}

?>