LINQ查询，选择最近的记录

Question

我们的表结构如下所示:

appointmentID    
1abc   --------------->1              
1abc (latest)  ------------>2            
1hjt               
990aa             
990aa              
990aa (latest             

---

DateTime start = DateTime.Now.AddDays(0);
DateTime end = DateTime.Now.AddDays(7));
List<JobCustomers> appointments = objectContext.JobCustomers.Where(
                    a => a.StartTime >= start && a.EndTime <= end && !string.IsNullOrEmpty(a.AppointmentId)).ToList();   
foreach (JobCustomers appointmentItem in appointments) {
    // HERE I WANT TO WRITE SOME CODE
    -- WHEN WE ARE INSERTING NEW RECORD OF A SAME ID EX "1abc" IT MUST 
    COMPARE WITH LATEST RECORD "-----2> 
}

---

我的要求:如果有超过1行具有相同的id，那么我需要通过预约id带来最近的记录如下

List<JobCustomers> appointments = objectContext.JobCustomers.Where(
                    a => a.StartTime >= start && a.EndTime <= end && !string.IsNullOrEmpty(a.AppointmentId).**take(0**)).ToList();

简单来说:当我们插入一个具有相同id的新记录时，使用LINQ，我们需要与最后插入的记录

Answer 1

LINQ和SQL都不知道插入数据的顺序，您需要有一个额外的字段来保存这个顺序(可以是日期，也可以是自动数字)。一旦你有了，你就可以使用:

YourList.OrderBy(i => i.Id).ThenByDescending(i => i.YourColumnToSaveOrder)

Answer 2

var latestAppts = appointments.GroupBy(x => x.AppointmentId)
                              .Select(g => g.Last());

Answer 3

如果我正确地阅读了这一点，您正试图特别抓取与所带来的相同ID的最新记录，这只需要用LINQ的LastOrDefault扩展方法完成:

//Variable 'yourNewRecord' is what you're about to enter into the database
var latestAppt = objectContext.JobCustomers
                              .LastOrDefault(a => a.StartTime >= start && 
                                                  a.EndTime <= end &&
                                                  a.AppointmentID.Equals(yourNewRecord.AppointmentID)

编辑:有关LastOrDefault的更多信息，请查看此处的MSDN链接