从linq检索重复值

本文介绍了从linq检索重复值的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

大家好，

我对linq语句有一些疑问.这是我的桌子，名为Tblactivity

activityid bigint
studentid bigint
activitydate datetime
说明nvarchar(Max)
状态位

我用数据填充Tblactivity.如

activityid |学生证|活动日期|描述|状态
1 | 1 | 2012-08-15 00:30:00 | descA | A
2 | 3 | 2012-08-16 12:30:00 | descAA | A
3 | 2 | 2012-08-16 13:15:12 | descB | B
4 | 3 | 2012-09-02 10:20:11 |说明| A
5 | 3 | 2012-09-02 11:00:00 |说明| A
6 | 4 | 2012-09-02 14:00:00 | descAA | S

所以我开发linq以获得学生ID = 3的详细信息.这是我的linq代码

Hi all,

I have some issue with linq statement. here is my table, named Tblactivity

activityidbigint
studentid bigint
activitydate datetime
descriptionnvarchar(Max)
statusbit

i populate Tblactivity with data. such as

activityid| studentid | activitydate | description | status
1| 1| 2012-08-15 00:30:00 | descA | A
2| 3| 2012-08-16 12:30:00| descAA | A
3| 2| 2012-08-16 13:15:12| descB | B
4| 3| 2012-09-02 10:20:11| descS | A
5| 3| 2012-09-02 11:00:00| descS | A
6| 4| 2012-09-02 14:00:00| descAA | S

so i develop linq to get detail information of student id = 3. here is my linq code

public List<Tblactivity> getStudents(long studentid, string status)
   {
	studentdatacontext db=new studentdatacontext;
            try
            {
                List<Tblactivity> BG = (from o in db.Tblactivities
                              orderby o.activitydate descending where o.studentid == studentid &&
                              o.activitydate.Value.Month <= DateTime.Now.Month &&
                              o.activitydate.Value.Month >= DateTime.Now.Date.AddMonths(-1)&&
                              o.status == status select o).ToList();

                return BG;
            }
            catch (Exception e)
            {
                throw e;
            }
        }

所以我根据学生ID = 3获得了所有记录，但是当活动日期相同(最新记录)时，我只想要一条记录.
我读了一些文章，他们建议我使用MAX().但我不知道如何发展以适应上述功能.请建议我.

谢谢，
df

so i got all of the records according to student id = 3.but i want only one record when the activitydate is same (the latest record).
i read some article they suggest me to use MAX(). but i don''t know how to develop to suit with the above function. pls suggest me.

Thanks,
df

推荐答案

List<Tblactivity> BG= (from o in db.Tblactivities
                                     where o.studentid == studentid &&
                                       o.activitydate.Value.Month <= DateTime.Now.Month &&
                                       o.activitydate.Value.Month >= DateTime.Now.Date.AddMonths(-1) &&
                                       o.status == status
                                       && o.activitydate == (from n in db.Tblactivities where n.studentid == o.studentid && Convert.ToString(n.activitydate).Substring(0, 10) == Convert.ToString(o.activitydate).Substring(0, 10) orderby n.activitydate descending select n).Max(l => l.activitydate)
                                   select o).Distinct().ToList();

List<tblactivity> BG = (from o in db.Tblactivities
                       orderby o.activitydate descending where o.studentid == studentid &&
                       o.activitydate.Value.Month <= DateTime.Now.Month &&
                       o.activitydate.Value.Month >= DateTime.Now.Date.AddMonths(-1)&&
                       o.status == status select o).ToList().Distinct();

这篇关于从linq检索重复值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！

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