public ActionResult Edit(int id)
        {
            var playlist = _context.Playlists.SingleOrDefault(p => p.PlaylistId == id);

            if (playlist == null)
            {
                return(HttpNotFound());
            }
            var songs = _context.Songs.Select(a => new
            {
                SongId = a.SongId,
                Name   = a.Name
            }).ToList();

            var defaultSelected = _context.Songs.Where(x => x.Playlists.Any(y => y.PlaylistId == id));

            int[] songsId = new int[defaultSelected.Count()];
            int   i       = 0;

            foreach (var a in defaultSelected)
            {
                songsId[i] = a.SongId;
                i++;
            }
            var viewModel = new PlaylistFormViewModel
            {
                Playlist = playlist,
                Songs    = new MultiSelectList(songs, "SongId", "Name"),
                SongId   = songsId
            };

            return(View("PlaylistForm", viewModel));
        }
        public ActionResult New()
        {
            var playlist = new Playlist();
            var songs    = _context.Songs.Select(a => new
            {
                SongId = a.SongId,
                Name   = a.Name
            }).ToList();
            var viewModel = new PlaylistFormViewModel
            {
                Playlist = playlist,
                Songs    = new MultiSelectList(songs, "SongId", "Name")
            };

            return(View("PlaylistForm", viewModel));
        }