Question

Is it possible to convert this code into one LINQ query. I could have sworn I had done something like this before, but I cannot figure out where I might that code might be. I want to perform a sub query and modify the values of the selected items if one list has values from another.

var selectInstructors = _instructorService.GetAllNonGuestInstructors()
                                          .Select(i => new SelectListItem()
                                                       {
                                                           Text = i.User.ToFullName(),
                                                           Value = i.Id.ToString() 
                                                       }).ToList();

var selectedItems = schedule.Instructors
                        .Select(instructior1 => selectInstructors.FirstOrDefault(s => s.Value == instructior1.Id.ToString()))
                        .Where(selectedItem => selectedItem != null);

foreach (var selectedItem in selectedItems )
{
    selectInstructors.Remove(selectedItem);
    selectedItem.Selected = true;
    selectInstructors.Add(selectedItem);
}

So let’s assume in the selectInstructors list I have these values:
John Smith, 1
Jane Doe, 2
Dave Ritter, 3
(before we iterate the persisted instructors the selected Boolean value is a default of false)

The schedule.Instructors class has the persisted list of instructors for that schedule:
John Smith, 1
Dave Ritter, 3

Now, what I would like to do is set any of the Selected properties in selectInstructors where the value is equal to schedule.Instructors

Answer 1

var selectedIds = schedule.Instructors.Select(i => i.Id.ToString()).ToList();    

var instructors = (from instructor in _instructorService.GetAllNonGuestInstructors()
                   let value = instructor.Id.ToString()
                   select new SelectListItem()
                   {
                       Text = instructor.User.ToFullName(),
                       Value = value,
                       Selected = selectedIds.Contains(value)
                   }).ToList();