Question

Having a problem retrieving a list of items from the database. This is what I am attempting.

List<SubjectAreaGroup> subjectAreas = examInstance.CurrentQuestionGroup.QuestionTypeGroups.Select(q => q.SubjectAreaGroups).toList();

But when I do this, it gives me an error that I can’t convert a SubjectAreaGroup List to a… SubjectAreaGroup List. If they are the same thing then why can’t I convert them?

Answer 1

I assume that the issue is due to the q.SubjectAreaGroups property giving a List<SubjectAreaGroup> for each QuestionTypeGroup. Thus, your Select statement is giving you a two-level sequence: IEnumerable<List<SubjectAreaGroup>>.

To resolve this, you simply need to flatten your resulting sequences into one sequence using the SelectMany operator:

List<SubjectAreaGroup> subjectAreas = 
    examInstance.CurrentQuestionGroup
                .QuestionTypeGroups
                .SelectMany(q => q.SubjectAreaGroups)
                .ToList();