public void Handle(DeleteCommentCommand command)
{
//TODO: the deleteComment needs optmistic lock -> add lesson version!!
//Lesson lesson = repo.GetById<Lesson>(command.Id, command.Version);
Lesson lesson = repo.GetById <Lesson>(command.Id);
lesson.DeleteComment(command.CommentId, command.Date);
repo.Save(lesson, Guid.NewGuid());
}