C＃Linq语句加入两个表和多列

Question

我有两个表; EndToEnd和PartPort。我想从EndToEnd中的同一行中获取PartPortA和PartportB数据，并使用它们查询Partport，并从Partport中获取其可能位于Partport表中任何行的PartGid。到目前为止，我可以做到这一点，但我必须做两个不同的LINQ调用，但我想将其降低到一个。这里是我的代码：

// 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); 

我想什么做的，我已经尝试过，但得到的错误是这样的：

   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(); 

我得到的错误是：

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“复杂”比较的加入，只是做一个笛卡尔乘积（from ... from），并通过where条款

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();