Linq2Sql连接到DefaultIfEmpty

Question

我有2个表格，我需要根据两个表格中的ClientID的cid来获取列。 我下面的代码可用于显示表，但_DOCID始终为null。 我想念什么？

            public IQueryable ReturnCart(int cid)
    {
        try 
        {
            var result = from c in veps.ecomCarts
                         join d in veps.lawFirmClientDocumentPurchaseds on c.ClientID equals d.ID into cd
                         from d in cd.DefaultIfEmpty()
                         where c.ClientID == cid
                            select new
                         {
                             _DOCID = d.ID,
                             _ID = c.ID,
                             _CID = c.ClientID,
                             _UPC = c.UPC,
                             _Description = c.Description,
                             _Quantity = c.Quantity,
                             _UnitPrice = c.UnitPrice,
                             _Discount = c.Discount,
                             _Total = c.Total,
                             _InProgress = c.InProgress,
                             _dts = c.dts

                         };


            return result;
        }
        catch (Exception ex)
        {
            _IsError = true;
            _ErrorMsg = ex.Message;
            return null;
        }
    }

更新的问题图片： 在此处输入图片说明

Answer 1

因此，经过多想，我意识到我的问题的答案是GroupBy Nested。 这是我的最终代码。

public IQueryable ReturnCart(int cid)
    {
        try 
        {
            var result = (from c in veps.ecomCarts
                          where c.ClientID == cid
                          select new 
                          {

                              _ID = c.ID,
                              _CID = c.ClientID,
                              _UPC = c.UPC,
                              _Description = c.Description,
                              _Quantity = c.Quantity,
                              _UnitPrice = c.UnitPrice,
                              _Discount = c.Discount,
                              _Total = c.Total,
                              _InProgress = c.InProgress,
                              _dts = c.dts,

                              lcdp = from d in veps.lawFirmClientDocumentPurchaseds
                                     select new
                                     {
                                         _DOCID = d.ID
                                     }
                          });

            return result;
        }
        catch (Exception ex)
        {
            _IsError = true;
            _ErrorMsg = ex.Message;
            return null;
        }
    }

谢谢Ivan发布。 您实际上帮助了我思考需要做什么。 非常感谢。