PDO——Call to a member function query() on a non-object

Think PHP在3.2之后好像就不支持PDO扩展了，然后我为了用PDO在控制层中写了一个php文件，里面只是写了实例化PDO的一段代码，我在控制请中引入这个文件，刚开始连接查询数据的时候没有错误，但是好像是有返回值的时候就报了一个——“**Call to a member function query() on a non-object**”的错误，有哪位了解的，请教下

pdo.class.php
<?php

$PDO = new PDO('mysql:host=localhost;dbname=cxshop', 'root', '',array(
    PDO::ATTR_PERSISTENT => true));

?>

CommonController.class.php
public function checkPDO($rolename,$mid=1){
        if (intval($mid) > 0) {
            require_once('Pdo.class.php');
            $res = $PDO->query("SELECT r_id as rid FROM `shop_role` where r_method='$rolename' limit 1");
            // 
            $roleres = $res->fetch(2);
            $checkmethID = $roleres['rid'];
            // dump($checkmethID);exit;

            $res = $PDO->query("SELECT gid FROM `shop_ag_access` where mid='$mid'");
            $agres = $res->fetchAll(2);
            if($checkmethID){
                foreach ($agres as $key => $value) {
                    $rges = $PDO->query("SELECT rid FROM `shop_rg_access` where gid='".$value['gid']."'");
                    $rges = $rges->fetchAll(2);
                    if (!$rges) {
                        return fasle;
                    }
                    $rgarr = array();
                    foreach ($rges as $kk => $val) {
                        $rgarr[] = $val['rid'];
                    }
                    $agres[$key]['gid'] = $rgarr;
                }
                $PDO = null;
                $arr = array();
                foreach ($agres as $key => $value) {
                    $arr[] = $value['gid'];
                }

                foreach ($arr as $key => $value) {
                    if (in_array($checkmethID, $value) == true) {
                        return true;
                    }
                }
                return false;
            }else{
                return false;
            }
        }else{
            return false;
        }
    }

Think PHP在3.2之后好像就不支持PDO扩展了，然后我为了用PDO在控制层中写了一个php文件，里面只是写了实例化PDO的一段代码，我在控制请中引入这个文件，刚开始连接查询数据的时候没有错误，但是好像是有返回值的时候就报了一个——“**Call to a member function query() on a non-object**”的错误，有哪位了解的，请教下

pdo.class.php
<?php

$PDO = new PDO('mysql:host=localhost;dbname=cxshop', 'root', '',array(
    PDO::ATTR_PERSISTENT => true));

?>

CommonController.class.php
public function checkPDO($rolename,$mid=1){
        if (intval($mid) > 0) {
            require_once('Pdo.class.php');
            $res = $PDO->query("SELECT r_id as rid FROM `shop_role` where r_method='$rolename' limit 1");
            // 
            $roleres = $res->fetch(2);
            $checkmethID = $roleres['rid'];
            // dump($checkmethID);exit;

            $res = $PDO->query("SELECT gid FROM `shop_ag_access` where mid='$mid'");
            $agres = $res->fetchAll(2);
            if($checkmethID){
                foreach ($agres as $key => $value) {
                    $rges = $PDO->query("SELECT rid FROM `shop_rg_access` where gid='".$value['gid']."'");
                    $rges = $rges->fetchAll(2);
                    if (!$rges) {
                        return fasle;
                    }
                    $rgarr = array();
                    foreach ($rges as $kk => $val) {
                        $rgarr[] = $val['rid'];
                    }
                    $agres[$key]['gid'] = $rgarr;
                }
                $PDO = null;
                $arr = array();
                foreach ($agres as $key => $value) {
                    $arr[] = $value['gid'];
                }

                foreach ($arr as $key => $value) {
                    if (in_array($checkmethID, $value) == true) {
                        return true;
                    }
                }
                return false;
            }else{
                return false;
            }
        }else{
            return false;
        }
    }