MVC

how to bind distinct value in dropdown using Entity Framework in mvc 3, mvc 4 razor control?

 

Controller:- 

 private UploadEntities db = new UploadEntities();
  public ActionResult Create()
        {
            ViewBag.Campaign = db.Assets.Select(r => r.Category).Distinct();
            return View();
        }

  View Page:-

@Html.DropDownList("Campaign", new SelectList(ViewBag.Campaign))