public void AddChoice(Choice choice, string topicId, string username) { var topic = dac.GetTopic(x => x.id == topicId); var now = DateTime.UtcNow; string newid = Guid.NewGuid().ToString(); Choice newChoice = new Choice() { Id = newid, Name = choice.Name, CraeteBy = username, }; var choicelist = topic.ChoiceList.ToList(); choicelist.Add(newChoice); topic.ChoiceList = choicelist; dac.UpdateTopic(topic); }