Symfony 1.4 doctrine从图像doSave（）更新

I'm using Symfony 1.4 and Doctrine, when I update a row with a form, it seems that the form not invoke doSave() method...

I use doSave() method when I upload an image and use sfThumbnail.

What can I do?

Example:

protected function doSave($con = null) {
parent::doSave($con);

$thumbnail = new sfThumbnail();
                    $thumbnail->loadFile($upload->getTempName());
                    $thumbnail->save();
}

You should do this in postSave(), it will be better there. Read this page of the doctrine documentation if you don't know what I'm talking about.