void AddOrUpdateInstructor(AchieveContext context, string courseTitle, string instructorName)
{
var crs = context.Courses.SingleOrDefault(c => c.CourseName == courseTitle);
var inst = crs.Instructors.SingleOrDefault(i => i.LastName == instructorName);
if (inst == null)
{
crs.Instructors.Add(context.Instructors.Single(i => i.LastName == instructorName));
}
}