public RedirectToActionResult AddExistingArtist(string artistName)
        {
            Artist artist = (from s in repo.Shows
                             from a in s.Artists
                             where a.Name.ToLower() == artistName.ToLower()
                             select a).Single();
            Show show = repo.Shows.OrderByDescending(s => s.ShowID).First();

            repo.AddArtist(show, artist);
            //show.Artists.Add(artist);
            return(RedirectToAction("AddArtist"));
        }