Question

所以，我有db.Pipeline和db.JobStatus的聚合（PipelineJobStatus）对于一个PipelineID，我可能有多个状态。我想找到最后一个，并在viewbag中调用它，以便在Edit.cshtml上预览我需要linq。我这样想：

 private IQueryable<StatusPipelineMerge> returnStatusOnID()
    {
        var test = (
           from users in db.PipelineJobStatus
           from pipe in db.Pipelines
               .Where(pipe => pipe.PipelineID == users.PipelineID).DefaultIfEmpty()
           from status in db.JobStatus
               .Where(statuses => statuses.JobStatusID == users.JobStatusID).DefaultIfEmpty()
           from fco in db.FCOes
                .Where(fcoes => fcoes.FCOID == pipe.FCOID)
           from client in db.Clients
           .Where(clients => clients.ClientID == pipe.ClientID)
           orderby users.CreatedTimeStamp descending
           select new StatusPipelineMerge
           {
               JobStatusName = status.JobStatusName
           }
            );
        return (test);
    }

我之所以放下原因，只是抓住堆栈上的第一个日期（FirstOrDefault）。我能这样做吗？或者我需要MAX功能？我正在使用EF6 谢谢！

Answer 1

当您按顺序排序FirstOrDefault()时（假设可能没有任何你想要的东西。

如果您订购升序，则会使用LastOrDefault()。

要么是好的，那就去使你的代码最容易理解。

Answer 2

简直就是这样：

private StatusPipelineMerge returnStatusOnID()
{
  var test = (from users in db.PipelineJobStatus
     orderby users.CreatedTimeStamp descending
     select new StatusPipelineMerge
     {
       JobStatusName = users.JobStatus.JobStatusName
     }).FirstOrDefault();
  return (test);
}

我不了解这些连接的需要，也没有理解＆＃34; left join＆＃34;处理PipelineJobStatus和JobStatus之间的这种关系。

Answer 3

使用着名的Northwind示例数据库和EF：

    var lastPurchaseCustomer =
(from o in Orders
 orderby o.OrderDate descending
 select new
 {
   TheID = o.Customer.CustomerID
 }).FirstOrDefault();

Console.WriteLine(lastPurchaseCustomer.TheID);

将此SQL发送到服务器：

SELECT TOP (1) 
[Project1].[C1] AS [C1], 
[Project1].[CustomerID] AS [CustomerID]
FROM ( SELECT 
    [Extent1].[CustomerID] AS [CustomerID], 
    [Extent1].[OrderDate] AS [OrderDate], 
    1 AS [C1]
    FROM [dbo].[Orders] AS [Extent1]
)  AS [Project1]
ORDER BY [Project1].[OrderDate] DESC

并打印（我也可以从Order.CustomerID获取，但这里也可以要求CompanyName，ContactName等）：

RATTC

Linq查询asp.net的最新状态

3 个答案: