LINQ查詢幫助

Question

我有以下的Linq查詢：

from workItem in WorkItem 
    join workItemHistory in WorkItemHistory on workItem equals workItemHistory.WorkItem 
    join ivSweepHistory in IVSweepHistory on workItemHistory equals ivSweepHistory.WorkItemHistory 
    where workItem.SerialNumber == "080106081985" 
    orderby ivSweepHistory.ReadTime descending 
select ivSweepHistory 

原樣，這個偉大的工程。但是，我想修改此以便我只檢索第一行而不是所有行。我將如何做到這一點？

謝謝。

Answer 1

把它放在Take中。

(from workItem in WorkItem 
    join workItemHistory in WorkItemHistory on workItem equals workItemHistory.WorkItem 
    join ivSweepHistory in IVSweepHistory on workItemHistory equals ivSweepHistory.WorkItemHistory 
    where workItem.SerialNumber == "080106081985" 
    orderby ivSweepHistory.ReadTime descending 
select ivSweepHistory)Take(1) 

Answer 2

var item = (from workItem in WorkItem 
      join workItemHistory in WorkItemHistory on workItem equals workItemHistory.WorkItem 
      join ivSweepHistory in IVSweepHistory on workItemHistory equals ivSweepHistory.WorkItemHistory 
      where workItem.SerialNumber == "080106081985" 
      orderby ivSweepHistory.ReadTime descending 
      select ivSweepHistory).first(); 

Answer 3

只需使用First()方法：

var query = // your query; 
var result = query.First(); 

如果有返回使用FirstOrDefault()來避免被拋出的異常沒有結果的可能性。

Answer 4

var allResults = from workItem in WorkItem 
    join workItemHistory in WorkItemHistory on workItem 
     equals workItemHistory.WorkItem 
    join ivSweepHistory in IVSweepHistory on workItemHistory 
     equals ivSweepHistory.WorkItemHistory 
    where workItem.SerialNumber == "080106081985" 
    orderby ivSweepHistory.ReadTime descending 
select ivSweepHistory 

var first = allResults.FirstOrDefault(); 

或者

(from workItem in WorkItem 
    join workItemHistory in WorkItemHistory on workItem 
     equals workItemHistory.WorkItem 
    join ivSweepHistory in IVSweepHistory on workItemHistory 
     equals ivSweepHistory.WorkItemHistory 
    where workItem.SerialNumber == "080106081985" 
    orderby ivSweepHistory.ReadTime descending 
select ivSweepHistory).FirstOrDefault(); 

你也可以使用First()，但如果查詢不返回任何結果，First()將拋出一個異常，而FirstOrDefault()會妥善處理的條件。