超级简单的MVC问题，它如何知道你正在编辑的对象的ID是什么?

Having trouble grasping this:

难以把握:

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Edit(Movie movieToEdit)
{

    var originalMovie = (from m in _db.MovieSet
                         where m.Id == movieToEdit.Id
                         select m).First();
[Accept