在linq-to-entities的一对多连接中只获得一条(最后一条)记录

我在linq-to-entities中有以下内容

clientprojects = (from p in this.SAPMappingEntities.SAP_Master_Projects join c in this.SAPMappingEntities.SAP_Master_ProjectPartners on c.project_no equals p.project_no where c.partner_name.Contains(clientstring) orderby p.start descending select new ClientProjects { client = c.partner_name, location = c.city +", "+c.region, project_no = c.project_no, start_dt = p.start, end_dt = p.finish }).Take(50).ToList(); 

我想更改此查询,以便每个SAP_Master_Project只获取具有最新update_dt的SAP_Master_ProjectPartners记录。 我怎样才能做到这一点?

编辑

有一个项目表,其中包含项目编号和项目详细信息,包括项目开始和结束日期。 有一个项目合作伙伴表,其中包含项目合作伙伴编号,名称,项目编号,更新日期和其他详细信息。

SAP_MASTER_PROJECT

project_no

开始

SAP_MASTER_PROJECTPARTNERS

partner_no

project_no

PARTNER_NAME

区域

update_dt

当用户在文本框中输入“ABC”时,我想要返回的信息是项目编号,项目开始日期,项目结束日期加上项目合作伙伴名称,城市和最近50个项目的最后一个项目合作伙伴记录的状态(基于开始日期)项目合作伙伴名称包含或类似“ABC”。

我确定有多种方法可以做到这一点,但是他的SQL给了我需要的结果:

 SELECT TOP 50 p.project_no, p.start, p.finish, c.partner_name, c.city, c.region FROM (select pp.project_no, pp.partner_name, pp.city, pp.region from SAP_Master_ProjectPartners pp where pp.partner_name LIKE @clientstring AND pp.update_dt = (select max(pp1.update_dt) from SAP_Master_ProjectPartners pp1 where pp1.project_no = pp.project_no)) c join SAP_Master_Projects p on (p.project_no = c.project_no) ORDER BY p.start DESC 

编辑#2 sql实际上返回了一些具有相同update_dt的项,所以我将sql修改为如下。 仍在努力转换为linq。

 SELECT TOP 50 p.project_no, p.start, p.finish, c.partner_name, c.city, c.region, c.update_dt, c.row_id FROM SAP_Master_Projects p join (select pp.project_no, pp.partner_name, pp.city, pp.region, pp.update_dt, pp.row_id from SAP_Master_ProjectPartners pp where pp.partner_name LIKE @clientstring AND pp.row_id = (select TOP 1 row_id from SAP_Master_ProjectPartners pp1 where pp1.project_no = pp.project_no order by update_dt DESC)) c on (p.project_no = c.project_no) where p.active_flag = 1 ORDER BY p.start DESC 

如果您在SAP_Master_ProjectsSAP_Master_ProjectPartners之间定义了实体关系,则此查询可能会更简单,因此连接可以是隐式的而不是显式的。

编辑因为你不能这样做,这样的事情可能会起作用(在where子句中使用let和进行逻辑连接):

 var clientProjects = ( from p in entities.SAP_Master_Projects let c = entities.SAP_Master_ProjectPartners .Where(cl => cl.partner_name.Contains(clientstring) && cl.project_no == p.project_no ) .OrderBy(cl => cl.update_dt) // Todo: Might need to be descending? .FirstOrDefault() where c != null orderby p.start descending select new ClientProjects { client = c.partner_name, location = c.city + ", " + c.region, project_no = c.project_no, start_dt = p.start, end_dt = p.finish } ) .Take(50) .ToList() ; 

听起来你正试图提出以下查询:

 SELECT * FROM MasterProjects p INNER JOIN (SELECT project_no, partner_name FROM ProjectPartners o WHERE o.update_dt = (SELECT MAX(update_dt) FROM ProjectPartners i WHERE i.project_no = o.project_no)) c ON p.project_no = c.project_no AND p.partner_name = c.partner_name 

我不完全确定如何将其转换为LINQ,但这是我最好的尝试:

 var clientprojects = from p in MasterProjects join c in ProjectPartners on p.project_no == c.project_no where c.partner_name == (from o in ProjectPartners where o.project_no == c.project_no and o.update_dt == (from i in ProjectParters where o.project_no = i.project_no select i.update_dt).Max() select o.partner_name).First(); 

上面的LINQ甚至可能无法编译,但希望它会向您发送正确的方向。

对不起,我不会说你的语言。 但是,例如,在MySql中你可以sort by update_dt DESC LIMIT 1添加sort by update_dt DESC LIMIT 1你可以这样做或者类似的东西吗?