ProductPageController.cs

    public class ProductPageController : PageControllerBase<ProductPage>
    {
        private readonly IRatingService ratingService;
        private readonly IRatingStatisticsService ratingStatisticsService;

        public ProductPageController()
        {
            ratingService = EPiServer.ServiceLocation.ServiceLocator.Current.GetInstance<IRatingService>();
            ratingStatisticsService = EPiServer.ServiceLocation.ServiceLocator.Current.GetInstance<IRatingStatisticsService>();
        }
        
        // Other controller code omitted for brevity ...
        
        private Rating AddRatingForProduct(ProductPage currentPage, int ratingValue)
        {
            var productReference = Reference.Create(currentPage.ContentGuid.ToString());
            Reference userReference = null;
            if (this.User.Identity.IsAuthenticated)
            {
                userReference = Reference.Create(this.User.Identity.Name);
            }
            else
            {
                userReference = Reference.Create(System.Guid.NewGuid().ToString());
            }

            var rating = new Rating(userReference, productReference, new RatingValue(ratingValue));

            return ratingService.Add(rating);
        }

        private Rating GetUserRatingForProduct(ProductPage currentPage)
        {
            Rating rating = null;

            if (this.User.Identity.IsAuthenticated)
            {
                var productReference = Reference.Create(currentPage.ContentGuid.ToString());
                var userReference = Reference.Create(this.User.Identity.Name);
                var criteria = new Criteria<RatingFilter>
                {
                    Filter = new RatingFilter
                    {
                        Targets = new List<Reference> { productReference },
                        Rater = userReference
                    },
                    PageInfo = new PageInfo { PageSize = 1 }
                };

                var ratingPage = ratingService.Get(criteria);
                rating = ratingPage.Results.FirstOrDefault();
            }

            return rating;
        }

        private RatingStatistics GetAverageRatingForProduct(ProductPage currentPage)
        {
            var productReference = Reference.Create(currentPage.ContentGuid.ToString());

            var criteria = new Criteria<RatingStatisticsFilter>
            {
                Filter = new RatingStatisticsFilter
                {
                    Targets = new List<Reference> { productReference }
                },
                PageInfo = new PageInfo { PageSize = 1 }
            };

            var ratingStatisticsPage = ratingStatisticsService.Get(criteria);
            return ratingStatisticsPage.Results.FirstOrDefault();
        }

        private ResultPage<RatingStatistics> GetPopularProducts()
        {
            var criteria = new Criteria<RatingStatisticsFilter>
            {
                PageInfo = new PageInfo { PageSize = 10, PageOffset = 0 },
                OrderBy = new List<SortInfo>
                {
                    new SortInfo(RatingStatisticsSortFields.Mean, false)
                }
            };

            var ratingStatisticsPage = ratingStatisticsService.Get(criteria);
            return ratingStatisticsPage;
        }
    }