获得CException错误

I'm new to Yii and I'm following the screencasts tutorial of Yii. I did everything on the video but I'm getting an error

"Property "Message.content" is not defined."

$this->message = $message->content;

Here's my GreetingController.php

class GreetingController extends Controller
{

    public $message = '';

    public function actionIndex()
    {
        $message = Message::model()->findByPk(3);
        $this->message = $message->content;
        $this->render('index', array('content'=>$this->message));
    }

What must be the problem?

There wont be a field called content in your table Message.