如何將這個SQL查詢重寫爲LINQ或EF對象查詢

Question

如何在LINQ中重寫或使用EF對象查詢？

select r.UserName, 
    (select count(*) from tbl1 where UserName = r.UserName) as tbl1Count, 
    (select max(CreatedDate) from tbl2 where UserName = r.UserName) as tbl2Date, 
    (select max(SomeDate) from tbl3 where UserName = r.UserName) as tbl3Date, 
    max(r.DateRegistered) as SomeDate   
from sometable r 
group by r.UserName 

Answer 1

嘗試此查詢

var objlist = (
    From a in Contex.UserName 
    From b in Contex.tbl1.where(x=>x.UserName==a.UserName).DefaultEmpty() 
    From c in Contex.tbl2.where(x=>x.UserName==a.UserName).DefaultEmpty() 
    From d in Contex.tbl3.where(x=>x.UserName==a.UserName).DefaultEmpty() 
    group a by a.UserName into pg  
    Select new { 
     UserName = pg.UserName,tbl1count=pg.Count(x=>x.tbl1id) 
     ,tbl2Date = pg.max(x=>x.CreatedDate) 
     ,tbl3Date = pg.max(x=>x.SomeDate) 
     ,SomeDate = pg.max(x=>x.DteRegistered) 
}).ToList(); 

Answer 2

請嘗試以下代碼

StackOverflowEntities db = new StackOverflowEntities(); 

     var result = (from p in db.SomeTables 
        join q in db.Table_1 on p.UserName equals q.UserName into Q 
        from q in Q.DefaultIfEmpty() 
        join r in db.Table_2 on p.UserName equals r.UserName into R 
        from r in R.DefaultIfEmpty() 
        join s in db.Table_3 on p.UserName equals s.UserName into S 
        from s in R.DefaultIfEmpty() 
        group new { p, q, r, s } by p.UserName into g 
        select new 
        { 
         UserName = g.Key, 
         tbl1Count = g.Count(w => w.q != null), 
         tbl2Date = g.Max(w => w.r.CreatedDate), 
         tbl3Date = g.Max(w => w.s.SomeDate), 
         SomeDate = g.Max(w => w.p.DateRegistered) 
        }).ToList();