ajax.php文件用pdo替换mysql_*后，记录插入不了

<?php

include_once('connect.php');
$act = htmlspecialchars($_GET['act']);
if ($act == 'update_position') {
if (!is_numeric($_GET['id']) || !is_numeric($_GET['x']) || !is_numeric($_GET['y']) || !is_numeric($_GET['z']))
die("0");

$id = intval($_GET['id']);
$x = intval($_GET['x']);
$y = intval($_GET['y']);
$z = intval($_GET['z']);

//mysql_query("UPDATE wishing_wall SET xyz='" . $x . "|" . $y . "|" . $z . "' WHERE id=" . $id);
$link->exec("UPDATE wishing_wall SET xyz='" . $x . "|" . $y . "|" . $z . "' WHERE id=" . $id);

echo "1";
}else if ($act == 'delete') {
$id = intval($_GET['id']);
//mysql_query("DELETE FROM `wishing_wall` WHERE `id` = " . $id . "");
$link->exec("DELETE FROM `wishing_wall` WHERE `id` = " . $id . "");
echo "1";
} else if ($act == 'add') {
$left = intval($_POST['left']);
$top = intval($_POST['top']);
$txt = stripslashes(trim($_POST['content']));
$txt = htmlspecialchars($txt, ENT_QUOTES);
// $txt = mysql_real_escape_string(strip_tags($txt), $link); //过滤HTML标签，并转义特殊字符
$txt = $link->quote(strip_tags($txt));
if (strlen($txt) < 1 || strlen($txt) > 100) {
echo '内容长度为1~100字符之间';
exit;
}

$user = stripslashes(trim($_POST['user']));
$user = htmlspecialchars($user, ENT_QUOTES);
//$user = mysql_real_escape_string(strip_tags($user), $link);
$user = $link->quote(strip_tags($user));
if (strlen($user) < 2 || strlen($user) > 30) {
echo '姓名长度为2~10字符之间';
exit;
}
$color_id = intval($_POST['color_id']);
if ($color_id < 0 or $color_id > 5) {
$color_id = rand(1, 5);
}
$time = date('Y-m-d H:i:s');
$zIndex = $_POST['zIndex'];
$xyz = '' . $left . '|' . $top . '|' . $zIndex;
//$query = mysql_query("insert into wishing_wall(content,name,color,xyz,addtime)values('$txt','$user','$color_id','$xyz','$time')");

$sql="INSERT INTO wishing_wall(content,name,color,xyz,addtime)VALUES('$txt','$user','$color_id','$xyz','$time')";
$query = $link->exec($sql);

if ($query) {
//echo mysql_insert_id($link);
echo $link->lastInsertId();
} else {
echo '出错了ba！';
}
}
?>