// you should be clear in your repository methods
// about exactly what related data is going to be returned.
// returnc courses including their students.
public Course GetCourseById(string courseId)
{
using var context = new ChinookContext(_contextOptions);
DataModel.Course dbCourse = context.Courses
.Include(c => c.CourseStudents)
.ThenInclude(cs => cs.Student)
.First(c => c.Id == courseId);
var course = new Course(dbCourse.Id, dbCourse.Name);
foreach (CourseStudent cs in dbCourse.CourseStudents)
{
course.Students.Add(new Student(cs.StudentId.ToString(), cs.Student.Name));
}
return(course);
}
// look at the Students property and persist any changes to it.
// any unrecognized students will be ignored
public void UpdateCourseMemberships(Course course)
{
using var context = new ChinookContext(_contextOptions);
DataModel.Course dbCourse = context.Courses
.Include(c => c.CourseStudents)
.ThenInclude(cs => cs.Student)
.First(c => c.Id == course.CourseId);
var dbStudents = course.Students
.Select(s => context.Students.Find(int.Parse(s.Id)))
.Where(s => s != null); // ignore the unrecognized ones
// if there is already a tracked entity for something you ask for with "Find",
// it will give that existing instance to you instead of sending a new query.
// three possible cases: a student being added that's not already there
// a student being removed that was in there until now
// a student still in the course that was before also
// exercise to the reader
context.SaveChanges();
}
