public IActionResult EditLesson(CreateLessonView model)
        {
            USOSContext context    = this.initContext();
            Lesson      editLesson = context.Lesson.Find(model.lessonID);

            if (model.lectureID != null)
            {
                editLesson.lecture = context.Lecture.Find(Convert.ToInt32(model.lectureID));
            }
            if (model.lecturerID != null)
            {
                editLesson.lecturer = _userManager.FindByNameAsync(model.lecturerID).Result;
            }
            var select = context.LessonsGroup.Where(x => x.lesson.ID == model.lessonID).Select(x => new LessonsGroup(x));

            context.LessonsGroup.RemoveRange(select);
            if (model.group != null)
            {
                foreach (int g in model.group)
                {
                    Group        group          = context.Group.Find(g);
                    LessonsGroup newLessonGroup = new LessonsGroup();
                    newLessonGroup.group  = group;
                    newLessonGroup.lesson = editLesson;
                    context.LessonsGroup.Add(newLessonGroup);
                }
            }
            context.Entry(editLesson.lecturer).State = EntityState.Unchanged;
            context.SaveChanges();
            return(RedirectToAction("Lessons", "Admin"));
        }