C＃外部应用于LINQ

如何在LINQ中实现外部应用？ 我有一点问题。

这是我正在使用的SQL查询。

SELECT u.masterID ,u.user ,h.created FROM dbo.Users u OUTER APPLY (SELECT TOP 1 * FROM UserHistory h where h.masterID = u.masterID ORDER BY created DESC) h 

Answer 1

 from u in Users join UserHistory on u.masterID equals h.masterID into h select new {u.masterID, u.user, h.created.OrderByDescending().First()} 

Answer 2

 from u in Users join UserHistory on u.masterID equals h.masterID into h select new { u.masterID, u.user, Created = h.Select(x => x.created).OrderByDescending(c => c).FirstOrDefault() } 

或者，与协会：

 from u in Users let created = u.UserHistories.Select(x => x.created).OrderByDescending(c => c).FirstOrDefault() select new { u.masterID, u.user, Created = created } 

Answer 3

外部应用产生左外连接的结果，
查询应该是：

 var q = from u in db.Users join h in db.UserHistory on u.masterID equals h.masterID into ps from p in ps.DefaultIfEmpty() select new { masterID = u.masterID ,user = u.user ,created = ps.OrderByDescending(x=>x.created).FirstOrDefault()==null?null:ps.OrderByDescending(x=>x.created).First().created };