public List <Artist> CreateArtistList() { List <Artist> artists = new List <Artist>(); List <Music> musics = musicService.GetAll(); HashSet <String> artistNames = new HashSet <String>(); foreach (Music music in musics) { artistNames.Add(music.Artist); } foreach (String artistName in artistNames) { List <Music> artistMusics = musicService.GetAllByArtist(artistName); Artist artist = new Artist(artistMusics[0].Artist, artistMusics); artists.Add(artist); } return(artists); }