public ProductQueryService(IProductRepository productRepository, IProductCategoryRepository productCategoryRepository,
                            IProductCategoryDiscountRepository productCategoryDiscountRepository, IMapper mapper)
 {
     this.productRepository                 = productRepository;
     this.productCategoryRepository         = productCategoryRepository;
     this.productCategoryDiscountRepository = productCategoryDiscountRepository;
     this.mapper = mapper;
 }