Question

我在此站点上寻找问题的答案，但找不到任何东西。

我以前的帖子很长，所以我会尝试改进它。

我有这个模型：

public class Product : EntityBase
    {
        public string Name { get; set; }
        //attribuitions
        ....
        //Url das images?

        public int? CategoryId { get; set; }
        public virtual Picture Picture { get; set; }
        //More attribuitions
        ....
}

我需要从mode加载一个属性，但是此属性是一个虚拟属性，我无法在我的lambda中实例化。我做到了

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;

            });

但是当我在注释行中运行上面的代码时，我得到了NullReference的异常。由于Picture我无法实例化它，因此发生了这种情况。我在.Where(First query)下面做了一个左联接，什么也没做。我尝试以这种方式放置.Include：_productRepository.Table.Include(pic => pic.Picture).GroupJoin，什么也没有。我在.Include之后尝试了.Where，但没有尝试。换句话说，我做了很多尝试，但没有得到。我没有尝试匿名。我该怎么办？我在做什么错？

EDIT1

如果我这样放置.Include

var qry = _productRepository.Table.Include(pic => pic.Picture).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,
                ................... //Attribuitions below

我认为我在qry.ForEach中不需要new Product()，对吗？那我该怎么办，我需要做一个new Product()吗？放一个include我不知道该怎么做或如何做。

Answer 1

检查是否在Picture中设置了ForEach。尽管问题很可能是由于您在对Picture的查询中未包含Product实体造成的。尝试在GroupJoin的条件下将其添加到Picture.Id == Product.PictureId。

您还可以使用更方便的.Include到eager load的{{1}}实体。

我收到一个错误，因为我无法实例化另一个对象

1 个答案: