public void AddStudentAdviser(string userName, int teacherId)
        {
            var student = _context.Student.Where(p => String.Equals(p.UserName, userName, StringComparison.CurrentCultureIgnoreCase)).SingleOrDefault();

            StudentAdviser studentAdviser = new StudentAdviser();

            if (student != null)
            {
                studentAdviser.StudentId = student.Id;
                studentAdviser.TeacherId = teacherId;
            }

            _context.StudentAdviser.Add(studentAdviser);
            _context.SaveChanges();
        }
        public void AddStudentCourse(string userName, int courseId)
        {
            var            student          = _context.Student.Where(p => String.Equals(p.UserName, userName, StringComparison.CurrentCultureIgnoreCase)).SingleOrDefault();
            var            CourseMaxStudent = _context.StudentCourse.Where(x => x.CourseId == courseId).Count();
            var            course           = _context.Course.FirstOrDefault(x => x.Id == courseId);
            StudentAdviser studentCourse    = new StudentAdviser();

            if (student != null)
            {
                if (CourseMaxStudent > course.MaxStudent)
                {
                    throw new BadRequestException("Course is full");
                }
                else if (course.TimeStar > DateTime.Now)
                {
                }
                studentCourse.StudentId = student.Id;
                studentCourse.TeacherId = courseId;
            }

            _context.StudentAdviser.Add(studentCourse);
            _context.SaveChanges();
        }