连接两个表和多个列的C# Linq语句

Question

我有两张桌子: EndToEnd和PartPort。我希望从PartPortA和PartportB中的同一行获取EndToEnd数据，并使用它们查询Partport，并从Partport获取相应的PartGid，这可能位于Partport表的任何行上。到目前为止，我能够做到这一点，但我必须做两个不同的LINQ调用，但我想把它减少到一个。这是我的代码：

    // 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);

我想做的是，我已经试过了，但有一个错误是：

                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

你不用用连接。如果您想加入一个“复杂”比较，只需制作一个笛卡尔乘积(from ... from)并通过一个where子句链接行。

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();