/// <summary>
        /// Adds courses to a Schedule and stores it in database
        /// </summary>
        public static async Task AddCourseToScheduleAsync(Schedule schedule, ICollection <SelectedCourse> selectedCourses)
        {
            using (var db = new DatabaseContext(_filename, _basePath))
            {
                foreach (var c in selectedCourses)
                {
                    db.Entry(c).State = EntityState.Added;
                    foreach (var u in c.Users)
                    {
                        if (u.SelectedCourse == null)
                        {
                            u.SelectedCourse  = c;
                            db.Entry(u).State = EntityState.Added;
                        }
                    }
                }
                await db.SaveChangesAsync();

                schedule.AddCourses(selectedCourses);
            }
        }