Question

我有一个表格AppointmentStatusHistory，格式如下：

AppointmentId   AppointmentStatusId   Date
========================================================
1               1                     2/1/2012 (2nd January)
1               2                     2/2/2012 (2nd February)

我目前针对此运行查询，以便在给定时间范围内为约会返回'最近'状态。

我的LINQ查询

items = (from t1 in db.AppointmentStatusHistories
         from t2 in db.TaskAppointments
                      .Where(o => (o.ID == t1.AppointmentId))
         from t3 in db.Tasks
                      .Where(o => (o.Task_ID == t2.Parent_Task_ID))
         where t1.Timestamp >= first && t1.Timestamp <= last
            && t3.Creator == user
         group t1 by t1.AppointmentId into grp
         select new UserAppointmentTargetModel
         {
             AppointmentId = grp.Key,
             AppointmentStatusId = grp.OrderByDescending(g => g.Timestamp)
                                      .FirstOrDefault()
                                      .AppointmentStatusId
    }
);

使用上述内容在first = 1/1/2012和last = 2/1/2012时返回 AppointmentStatusId 状态为“1”。

要求

我希望有人可以就修改此问题给我一些建议以满足以下条件：

如果最新状态在当前时段内，包括记录。
如果没有，从结果集中省略。

Answer 1

您只需将过滤的last部分移至分组/获胜者之后。

db.AppointmentStatusHistories
.Where(ash => first <= ash.TimeStamp) //omit all records that are before the range
.Where(ash => ash.Appointment.TaskAppointments.Any(ta => ta.Task.Creator == user))
.GroupBy(ash => ash.AppointmentId)
.Select(g => g.OrderByDescending(ash => ash.TimeStamp).First()) //pick a winner
.Where(ash => ash.TimeStamp <= last) //omit winners that are after the range
.Select(ash => new UserAppointmentTargetModel()
{
  AppointmentId = ash.AppointmentId,
  AppoinementStatusId = ash.AppointmentStatus,
  Date = ash.Timestamp
}

（上述强制性查询理解语法形式）

from ash in db.AppointmentStatusHistories
where first <= ash.TimeStamp
where ash.Appointment.TaskAppointments.Any(ta => ta.Task.Creator == user)
group ash by ash.AppointmentId into g
let winner = g.OrderByDescending(ash => ash.TimeStamp).First()
where winner.TimeStamp <= last
select new UserAppointmentTargetModel()
{
  AppointmentId = winner.AppointmentId,
  AppoinementStatusId = winner.AppointmentStatus,
  Date = winner.Timestamp
}

附注：

我使用导航属性来进行用户过滤。如果你无法使用它，请返回连接。

在群组中呼叫First始终是安全的。团体不是空的。在这种情况下，不需要FirstOrDefault。

我重复使用方法样式查询中的ash变量名称来传达类型，因为它是在未声明类型的两个不同位置声明的。我在理解风格查询中将其更改为winner以更好地传达意图，因为它在一个可以通过检查验证类型的地方声明。

另外，我从不使用＆gt; =日期。它只能导致悲伤。

分组并仅返回LINQ查询中的最新记录

1 个答案: