create.cs

        public RatingDTO Create(Guid userId, Guid whiskeyId, int score, string review = "")
        {
            using(IUnitOfWork uow = _unitOfWorkFactory.Create("RatingService.Create"))
            {
                Rating r = uow.RatingRepository.All().Where(x => x.ReviewOf.Id == whiskeyId && x.ReviewedBy.Id == userId).FirstOrDefault();

                Whiskey w = uow.WhiskeyRepository.FindById(whiskeyId);
                User u = uow.UserRepository.FindById(userId);

                // there is no existing Rating in the system, so create a new one.))
                if(r == null)
                {
                    r = uow.RatingRepository.Create(w, u, score);
                }

                r.Review = review;

                UpdateScores(w);

                uow.Save();

                return RatingDTO.Create(r);
            }
        }