在mysql数据库上插入PHP不能使用PDO（带有预处理语句）

Question

我正在用DropzoneJS做一个简单的网站来上传文件，并在我的数据库中插入一些关于上传者的信息，文件类型等。
但问题是我在'upload_log'中没有看到任何内容文件上传后的表格 这是我的upload.php代码：

$ds = DIRECTORY_SEPARATOR;
    $foldername = "../common/uploads";

    if (!empty($_FILES)) {
        $fileupload = basename( $_FILES['file']['name']);
        $fileType = $_FILES['file']['type'];
        $fileSize = $_FILES['file']['size'];

        $tempFile = $_FILES['file']['tmp_name'];
        $targetPath = dirname( __FILE__ ) . $ds. $foldername . $ds;
        $targetFile =  $targetPath. $fileupload;
        move_uploaded_file($tempFile,$targetFile);
        $upload_info = "Filetype : <b>".$fileType."</b> <br>File size : <b>".$fileSize."</b><br>File name : <b> ".$fileupload."</b>";
        add_to_log($_SESSION['username'], 'upload', $upload_info);
    }

函数“add_to_log”：

function add_to_log($usr, $type, $info) {
$servername = 'localhost';
$dbname = 'foo';
$username = 'root';
$password = 'foo';
try
{
    $bdd = new PDO('mysql:host='.$servername.';dbname='.$dbname.'', $username, $password);
}
catch(Exception $e)
{
        die('DB error');
}
$req = $bdd->prepare('INSERT INTO upload_log(type, user, info) VALUES(:type, :user, :info)');
$req->execute(array(
    'type' => $type,
    'user' => $user,
    'info' => $info
    ));
}