C＃Linq語句加入兩個表和多列

Question

我有兩個表; EndToEnd和PartPort。我想從EndToEnd中的同一行中獲取PartPortA和PartportB數據，並使用它們查詢Partport，並從Partport中獲取其可能位於Partport表中任何行的PartGid。到目前爲止，我可以做到這一點，但我必須做兩個不同的LINQ調用，但我想將其降低到一個。這裏是我的代碼：

// this demonstrates how to join two tables, however only works for one AssetportGid at a time 
    var part_portGid_a_results = (from icp in entities.EndToEnd 
        where icp.IntertPortGidA != null && 
        icp.IntertPortGidB != null 
        join ica in entities.PartPort 
        on icp.PartPortA equals ica.PortGid 
        select new { icp.PartPortA, ica.PartGid, }).ToList(); 

    var part_portGid_b_results = (from icp in entities.EndToEnd 
            where icp.IntertPortGidA != null && 
            icp.IntertPortGidB != null 
            join ica in entities.PartPort 
            on icp.PartPortB equals ica.PortGid 
            select new { icp.PartPortA, ica.PartGid, }).ToList(); 



    return Json(part_portGid_a_results, JsonRequestBehavior.AllowGet); 

我想什麼做的，我已經嘗試過，但得到的錯誤是這樣的：

   var part_portGid_a_results = (from icp in entities.EndToEnd 
        where icp.IntertPortGidA != null && 
        icp.IntertPortGidB != null 
        join ica in entities.PartPort 
        on icp.PartPortA && icp.PartPortB equals ica.PortGid 
        select new { icp.PartPortA, ica.PartGid, }).ToList(); 

我得到的錯誤是：

Guid? EndToEnd.PartPortB 

Error: 
    Operator '&&' cannot be applied to operands of type 'System.Guid' and 'System.Guid?' 

Answer 1

你不要有使用加入。如果你想用「複雜」比較的加入，只是做一個笛卡爾乘積（from ... from），並通過where條款

var part_portGid_results = (from icp in entities.EndToEnd 
          where icp.IntertPortGidA != null && 
          icp.IntertPortGidB != null 
          from ica in entities.PartPort 
          where icp.PartPortA == ica.PortGid 
           || icp.PartPortB == ica.PortGid 
          select new { icp.PartPortA, ica.PartGid, }).ToList();