Virtual property is not instantiated in lambda

Question

When I took a code to improve performance I had the following. A method GetAll() this method populated a var. It was made a foreach in this var and was assigning the appropriate values. It happens that within this foreach there was such a command:

if (product.PictureId.HasValue)
    item.PictureFilename = product.Picture.FileName;

This condition is paramount. The problem that this foreach takes at least 4 min to execute and I speak of only 122 records (202 in Getall()). I did a lambda and reduced in Debug to 17s and environment to 6s to 10s. But the problem is in the code above. In lambda I can’t bring it: product.Picture.FileName. Picture is a virtual property of Product(class) and Picture is a class as well. The lambda is not the instance and gives error of NullReferenceException, of the kind:

Undefined object reference for an object instance.

There is some understanding missing in Linq/Lambda for me to complete this topic. This is the complete lambda that I did and the commented lines are the ones that are giving problem. Besides what I posted (original Lambda), I made several other attempts.

var qry = _productRepository.Table.GroupJoin(_categoriesRepository.Table,
            p => p.CategoryId,
            c => c.Id,
            (p, c) => new { Product = p, Categories = c.DefaultIfEmpty() })

            .Where(hdg => hdg.Product.Hidden == false)
            .SelectMany(final => final.Categories,
            (final, c) => new CatalogItemResponse
            {
                ChildrenCategoryId = final.Product.ChildrenCategoryId,

                DolarRate = 0.0m,
                ResellerPriceUSD = 0.0m,
                ResellerPriceBRL = 0.0m,
                BasePriceBRL = 0.0m,
                BasePriceUSD = 0.0m,

                CategoryId = final.Product.CategoryId,
                CategoryName = (c != null ? c.Name : null),
                PictureId = final.Product.PictureId,
                Description = final.Product.Description,
                ShortDescription = final.Product.ShortDescription,
                Name = final.Product.Name,
                NameHtml = string.IsNullOrEmpty(final.Product.NameHtml) ? final.Product.Name : final.Product.NameHtml,
                PartNumber = final.Product.PartNumber,
                Hidden = final.Product.Hidden,
                Order = final.Product.Order,
                HaveMaximumPercentage = final.Product.HaveMaximumPercentage,
                MaximumPercentage = final.Product.MaximumPercentage,
                HaveMinimumPercentage = final.Product.HaveMinimumPercentage,
                MinimumPercentage = final.Product.MinimumPercentage,
                AuthorizeMaximumPercentageAlteration = final.Product.AuthorizeMaximumPercentageAlteration,
                AuthorizeMinimumPercentageAlteration = final.Product.AuthorizeMinimumPercentageAlteration,
                StandardMarkup = final.Product.StandardMarkup,
                DistributionCenterErpId = final.Product.DistributionCenterErpId,
                PictureFilename = final.Product.Picture.FileName

            }).ToList();

            qry.ForEach(q =>
            {
                var product = new Product();

                product.CategoryId = q.CategoryId;
                product.AuthorizeMaximumPercentageAlteration = q.AuthorizeMaximumPercentageAlteration;
                product.AuthorizeMinimumPercentageAlteration = q.AuthorizeMinimumPercentageAlteration;
                product.HaveMaximumPercentage = q.HaveMaximumPercentage;
                product.HaveMinimumPercentage = q.HaveMinimumPercentage;
                product.Hidden = q.Hidden;
                product.ChildrenCategoryId = q.ChildrenCategoryId;
                product.Description = q.Description;
                product.DistributionCenterErpId = q.DistributionCenterErpId;
                product.MaximumPercentage = q.MaximumPercentage;
                product.MinimumPercentage = q.MinimumPercentage;
                product.Name = q.Name;
                product.NameHtml = q.NameHtml;
                product.Order = q.Order;
                product.PartNumber = q.PartNumber;
                product.PictureId = q.PictureId;
                product.ShortDescription = q.ShortDescription;
                product.StandardMarkup = q.StandardMarkup;

                var parentProducts = _productService.GetParentsOf(product.Id).Select(x => x.PartNumber);
                q.Parents.AddRange(parentProducts);

                //if (product.PictureId.HasValue)
                //    q.PictureFilename = product.Picture.FileName;

                var price = _erpPriceService.GetPrice(product, 1, resellerId).Result;

                if (price.BasePriceUSD > 0)
                    q.DolarRate = price.BasePriceBRL / price.BasePriceUSD;

                q.ResellerPriceUSD = price.ResellerPriceUSD;
                q.ResellerPriceBRL = price.ResellerPriceBRL;
                q.BasePriceBRL = price.BasePriceBRL;
                q.BasePriceUSD = price.BasePriceUSD;

            });

            return qry;

Answer 1

Watching your code I see that variable product is receiving a new instance var product = new Product() but at no time was a value assigned to product.Picture then it is null (unless you have assigned value in the empty constructor of the class Product), in this case if you access any Picture property you will receive Exception: "Object reference not set for an instance of an object". In case you have activated the LazyLoading within the Query you can load the virtual properties automatically, in your case the code I just mentioned is outside the query generation because it ended when you performed the 'Immediate Execution' through the ToList().