使用Linq将每天最早的条目分组

Question

试图让我的头围绕Linq,同时记录我早上登录的时间,这应该是我进入办公室的时间.

到目前为止我的代码是:

EventLog SecurityLog = new EventLog("Security");

var AccountLoggedOnEntries = SecurityLog.Entries.Cast<EventLogEntry>()
    .Where(x => x.InstanceId == 4624)
    .Select(x => new
    {
        DateGenerated = x.TimeGenerated.ToShortDateString()
        ,
        TimeGenerated = x.TimeGenerated.ToShortTimeString()
        ,
        x.Message
    })
    .ToList();

DgvLogSummary.DataSource = AccountLoggedOnEntries;

DgvLogSummary.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.DisplayedCells;

我想过滤结果,这样我每天只有一个条目,这是最早的时间.

在SQL中,我通常会使用最早条目的消息,然后按所有字段分组.

如何在Linq中执行类似的查询？

Answer 1

在LINQ中,您可以分组,对每个组进行排序,然后选择第一个项目:

var AccountLoggedOnEntries = log.Entries.Cast<EventLogEntry>()
    .Where(x => x.InstanceId == 4624)
    .GroupBy(x => x.TimeGenerated.Date)
    .Select(g => g.OrderBy(x => x.TimeGenerated).First())
    .Select(x => new {
        DateGenerated = x.TimeGenerated.ToShortDateString()
    ,   TimeGenerated = x.TimeGenerated.ToShortTimeString()
    ,   x.Message
    })
    .ToList();