private void saveTournamentButton_Click(object sender, EventArgs e) { TournamentController tournamentController = new TournamentController(); List <int> addchanges = this.tempTournamentPlayers.Select(player => player.Id).Where(id => this.TournamentPlayers.Select(tplayer => tplayer.Id).Contains(id)).ToList(); foreach (int change in addchanges) { MessageBox.Show(change + ""); tournamentController.AddTournamentEntry(change, this.Tournament.Id); } List <int> removechanges = this.tempAllPlayers.Select(player => player.Id).Where(id => !this.AllPlayers.Select(tplayer => tplayer.Id).Contains(id)).ToList(); foreach (int change in removechanges) { tournamentController.RemoveTournamentEntry(change, this.Tournament.Id); } UpdateTournament?.Invoke(); }