映射列表未从主列表中获取所有项目

Question

我正在出口32,000种产品，但是有一个奇怪的问题，retList仅获得1917个项目，我不知道为什么会这样。

 private List<FTradeItemsExport> MapTradeItems(List<TradeItems> tradeItem)
    {
        List<TradeItemsExport> retList = new List<TradeItemsExport>();
        try
            {

                var StockImport = new Fuel_StockItemImports();


                List<StandardLookUpList> _AnalsisCodes = GetAnayalsisCodesForExportCode();

                StandardLookUpList sport = new StandardLookUpList();
                StandardLookUpList gender = new StandardLookUpList();
                StandardLookUpList colour = new StandardLookUpList();
                StandardLookUpList Size = new StandardLookUpList();
                StandardLookUpList categorycode = new StandardLookUpList();
                StandardLookUpList categorydesc = new StandardLookUpList();
                StandardLookUpList subcategorycode = new StandardLookUpList();
                StandardLookUpList subcategorydesc = new StandardLookUpList();

                StandardLookUpList brandcode = new StandardLookUpList();
                StandardLookUpList branddesc = new StandardLookUpList();


                foreach (var item in tradeItem)
                {

                    var codesForThisItem = _AnalsisCodes.Where(w => w.ItemCode == item.ItemCode);
                    if (codesForThisItem.Any())
                    {
                        sport = codesForThisItem.FirstOrDefault(x => x.code == Constants.Sport);

                        gender = codesForThisItem.FirstOrDefault(x => x.code == Constants.Gender);
                        colour = codesForThisItem.FirstOrDefault(x => x.code == Constants.Colour);
                        Size = codesForThisItem.FirstOrDefault(x => x.code == Constants.Size);
                        categorycode = codesForThisItem.FirstOrDefault(x => x.code == Constants.Colour);
                        categorydesc = codesForThisItem.FirstOrDefault(x => x.code == Constants.Category);

                        subcategorycode = codesForThisItem.FirstOrDefault(x => x.code == Constants.Category);
                        subcategorydesc = codesForThisItem.FirstOrDefault(x => x.code == Constants.SubCategory);
                        brandcode = codesForThisItem.FirstOrDefault(x => x.code == Constants.Brand);
                    }
                    retList.Add(new  TradeItemsExport()
                    {
                        ItemCode = item.ItemCode,
                        BarCode = item.BarCode,
                        Description = item.Description,
                        SupplierCode = item.SupplierCode,
                        SupplierStockCode = item.SupplierStockCode,
                        Product_Group_Code = "",
                        Product_Group_Desc = "",
                        SportCode = sport.LookupValue.ToStringOrEmpty(),
                        SportDesc = sport.description.ToStringOrEmpty(),
                        GenderCode = gender.LookupValue.ToStringOrEmpty(),
                        GenderDesc = gender.description.ToStringOrEmpty(),
                        ColourCode = colour.LookupValue.ToStringOrEmpty(),
                        ColourDesc = colour.description.ToStringOrEmpty(),
                        SizeCode = Size.LookupValue.ToStringOrEmpty(),
                        SizeDesc = Size.description.ToStringOrEmpty(),
                        CategoryCode = categorycode.LookupValue.ToStringOrEmpty(),
                        CategoryDesc = categorydesc.description.ToStringOrEmpty(),
                        subcategorycode = subcategorycode.LookupValue.ToStringOrEmpty(),
                        subcategorydesc = subcategorydesc.description.ToStringOrEmpty(),
                        BrandsCode = brandcode.LookupValue.ToStringOrEmpty(),
                        BrandsDesc = branddesc.description.ToStringOrEmpty(),
                        Vat = item.Vat,
                        GrossWeight = item.Weight,
                        CommodityCode = item.CommodityCode,
                        price_exVAT = item.price_exVAT,
                        price_incVAT = item.price_incVAT,
                        currentprice_exVAT = item.currentprice_exVAT,
                        currentprice_incVAT = item.currentprice_incVAT,
                        creation_date = item.creation_date,
                        Inactive_date = item.Inactive_date,
                        status = 1



                    });
                    var Stock = new Fuel_StockItemImport();



                    Stock.StockItem = item.ItemCode;
                    Stock.IsProcessed = true;
                    Stock.DateImported = DateTime.Now;
                    StockImport.Add(Stock);
                    StockImport.Update();


                }


            }
            catch (Exception ex)
            {

            }
            return retList;


    }

如您所见，下面是映射列表中预期的项目的真实数字，我没有理解，因为我没有在数据上获得任何例外？当我单步执行代码并检查刹车点时，它没有用空引用轰炸到任何地方，因此无法确定发生了什么。

Answer 1

发生这种情况的唯一方法是，在精确插入1912个项目之后，您将忽略循环中间的异常。

最可能的原因是在构造ToStringOrEmpty()对象时调用TradeItemsExport。您可以使用?.运算符来解决此问题。

通常，您不应该忽略catch (Exception ex) { }不执行任何操作的所有异常。如果您不知道如何处理异常，则不应有捕获该异常的代码。在这种情况下，这显然是编程问题（无法对对象进行null检查），因此应完全删除try / catch。

  

（摘自评论）是否有更快的合并方法？

通过将Where(w => w.ItemCode == item.ItemCode)替换为字典中基于哈希的查找，可以大大提高速度：

var byItemCode = _AnalsisCodes
    .GroupBy(w => w.ItemCode)
    .ToDictionary(g => g.Key, g => g.First());
...
foreach (var item in tradeItem) {
    if (byItemCode.TryGetValue(item.ItemCode, out var codesForThisItem) && codesForThisItem.Any()) {
        ...
    }
}

如果这样做不能充分加快速度，则需要在进入循环之前通过设置字典来重新组织codesForThisItem内部的查找。