c# - 允许组中的空表

Question

我正在尝试用 C# 表达式编写一个 LINQ 查询，以获取采购订单的概述，其中包括一个包含采购订单TblPODetails中项目列表的表。我想获取此表中的每个行项目，然后将已收到的项目总数添加到表中TblPOReceipts。如果没有收到任何项目，则TblPOReceipts显示 null 并且查询返回 0 个结果。

我怎样才能在 中允许空值TblPOReceipts并且仍然从 中获得我的其余结果TblPODetails？

这是我的查询：

from podetail in TblPODetails
from pricebook in TblPriceBooks.Where(x => x.ItemID == podetail.ItemID).DefaultIfEmpty()
from receipt in TblPOReceipts.Where(x => x.ItemID ==podetail.ItemID).DefaultIfEmpty()

where podetail.PONumber == 4707
where receipt.PONumber == 4707

group new { receipt, podetail, pricebook } by new {pricebook, podetail, receipt.QuantityReceived } into g

select new {
    g.Key.podetail.ItemDescription,
    TotalReceived = g.Sum (x => x.receipt.QuantityReceived),
    QuantityPosted = g.Where (x => x.receipt.Posted == true).Sum (x => x.receipt.QuantityReceived),
    g.Key.podetail.ItemID,
    g.Key.podetail.QuantityOrdered,
    g.Key.podetail.ProjectedCost,
    g.Key.podetail.TotalProjectedCost,
    g.Key.pricebook.BaseCost,
    g.Key.pricebook.ItemURL
}

Answer 1

在我使用的查询中，这是一个愚蠢的错误：

where receipt.PONumber == 4707

这是空的，因此不返回任何结果。

我已经解决了这个问题：

where receipt.PONumber == null || receipt.PONumber == 4707

我也将总和转换为 int。

    TotalReceived = (int?)g.Sum (x => x.receipt.QuantityReceived),
    QuantityPosted = (int?)g.Where (x => x.receipt.Posted == true).Sum (x => x.receipt.QuantityReceived),