Entity framework savechanges error - asp.net-mvc

Question

I have a wizard step in which a user fills in fields. I then use json to save the values into my database for each wizard step.
However, in my repository I have my savechanges(). But it wont save the changes, instead it throws an error:
Entities in 'NKImodeledmxContainer.SelectedQuestion' participate in the 'QuestionSelectedQuestion' relationship. 0 related 'Question' were found. 1 'Question' is expected.
Anyone know how to get rid of the error? Do I have to get the ID from Question and save it aswell to my database or can I change something in EF so the error message is not getting thrown?
This is my post in my controller:
[HttpPost]
public JsonResult AnswerForm(int id, SelectedQuestionViewModel model)
{
bool result = false;
var goalCardQuestionAnswer = new GoalCardQuestionAnswer();
goalCardQuestionAnswer.SelectedQuestion = new SelectedQuestion();
goalCardQuestionAnswer.SelectedQuestion.Id = model.QuestionID;
goalCardQuestionAnswer.Comment = model.Comment;
goalCardQuestionAnswer.Grade = model.Grade;
if (goalCardQuestionAnswer.Grade != null)
{
answerNKIRepository.SaveQuestionAnswer(goalCardQuestionAnswer);
answerNKIRepository.Save();
result = true;
return Json(result);
}
answerNKIRepository.SaveQuestionAnswer(goalCardQuestionAnswer);
answerNKIRepository.Save();
return Json(result);
}
My Repository
public class AnswerNKIRepository
{
private readonly NKImodeledmxContainer db = new NKImodeledmxContainer();
public List<SelectedQuestion> GetAllSelectedQuestionsByGoalCardId(int goalCardId)
{
return db.SelectedQuestion.Where(question => question.GoalCard.Id == goalCardId).ToList();
}
public void SaveQuestionAnswer(GoalCardQuestionAnswer goalCardQuestionAnswer)
{
db.GoalCardQuestionAnswer.AddObject(goalCardQuestionAnswer);
}
public void Save()
{
db.SaveChanges();
}
}
This is my ViewModel:
public class SelectedQuestionViewModel
{
public int? Grade { get; set; }
public string Comment { get; set; }
public string SelectedQuestionText { get; set; }
public int QuestionID { get; set; }
}
This is my database model:

Answer 1

The exception complains that SelectedQuestion.Question is a required navigation property but you don't set this property in your code. Try to load the question by Id from the repository and set it to the SelectedQuestion.Question reference: Replace this line ...
goalCardQuestionAnswer.SelectedQuestion.Id = model.QuestionID;
...by...
goalCardQuestionAnswer.SelectedQuestion.Question =
answerNKIRepository.GetQuestionById(model.QuestionID);
And in your repository add the method:
public Question GetQuestionById(int id)
{
return db.Question.Single(q => q.Id == id);
}