public void Handle(AddNewRatingCommand command)
{
//Lesson lesson = repo.GetById<Lesson>(command.Id, command.Version);
Lesson lesson = repo.GetById <Lesson>(command.Id);
lesson.AddNewRating(command.RatingId, command.Rating, command.UserId, command.Content, command.Date);
repo.Save(lesson, Guid.NewGuid());
}