public void Apply(Guid courseId, Guid userId)
{
//basic guard clauses
if (!_coursesRepository.CourseExists(courseId))
{
throw new ArgumentException();
}
if (!_userRepository.UserExists(userId))
{
throw new ArgumentException();
}
var user = _userRepository.FindById(userId);
var course = _coursesRepository.FindById(courseId);
//this prevents the user from applying multiple times
//I could also consider throwing something like UserAlreadyAppliedException in this case
if (!CheckIfUserHasAlreadyApplied(user, course))
{
course.AppliedUsers.Add(user);
}
}
