Question

我有以下Linq查询：

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

原样，这很有用。但是，我想修改它，以便我只检索第一行而不是所有行。我该怎么做？

感谢。

Answer 1

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 2

只需使用First()方法：

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

如果可能没有返回任何结果，请使用FirstOrDefault()来避免抛出异常。

Answer 3

将其封入Take。

(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 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();

您也可以使用First()，但如果查询无法返回任何结果，First()将抛出异常，而FirstOrDefault()将优雅地处理该条件。

LINQ查询帮助

4 个答案: