Linq left join 怎么写？？？ 求正解！

[Jueyoung]

要求 分别实现类似以下两种情况的 Linq 语句

谢谢！

select * 
from table1
left join table2 on table1.Id = table2.empId
left join table3 on table2.deptId = table3.deptId
where table1.id > 10

select * 
from table1
left join table2 on table1.Id = table2.empId
left join table3 on table1.deptId = table3.deptId
where table1.id > 10

[Jueyoung]

么有人呢？

[醉爱]

1)
var tb = from tb1 in table1
join tb2 in table2 on tb1.Id equals tb2.empId into ggg
from gg in ggg.DefaultIfEmpty()
join tb3 in table3 on gg.deptId equals tb3.deptId into kkk
from kk in kkk.DefaultIfEmpty()
where (tb1.Id > 10)
select new
{
tb1.id
...
kk.deptId
...
};
2)
var tb = from tb1 in table1
join tb2 in table2 on tb1.Id equals tb2.empId into ggg
from gg in ggg.DefaultIfEmpty()
join tb3 in table3 on tb1.deptId equals tb3.deptId into kkk
from kk in kkk.DefaultIfEmpty()
where (tb1.Id > 10)
select new
{
tb1.id
...
kk.deptId
...
};

[Jueyoung]

但是这样写 我用 tb.FirstOrDefault() 就出错呢？

[醉爱]

你先看看tb里面有没有值

[q107770540]

使用DefaultIfEmpty 翻译成SQL语句不是LEFT JOIN，而是LEFT OUT JOIN

[q107770540]

//1 .
  DbContext db=new DbContext ();
        var q=from t1 in db.Table1
              join t2 in db.Table2
              on t1.Id equals t2.empId 
              join t3 in db.Table3
              on t2.deptId equals t3.detpId
              where t1.id>10
              select new {t1.id,t1......}


//2

  DbContext db=new DbContext ();
        var q=from t1 in db.Table1
              join t2 in db.Table2
              on t1.Id equals t2.empId 
              join t3 in db.Table3
              on t1.deptId equals t3.detpId
              where t1.id>10
              select new {t1.id,t1......}

[wuyq11]

var q =
from e in db.Employees
join o in db.Books on e.EmployeeID equals o.EmployeeID into b
from x in b.DefaultIfEmpty()
select new
{
e.ID,
e.Name,
o.BookName
};

[Jueyoung]

谢谢各位 我要逐一再试一试

[Jueyoung]

[Quote=引用 6 楼 q107770540 的回复:]

C# code

//1 .
DbContext db=new DbContext ();
var q=from t1 in db.Table1
join t2 in db.Table2
on t1.Id equals t2.empId
join t3 in db.Table3
……
[/Quote]


这样貌似就是 inner join 了呀

[Jueyoung]

LINQ to Entities does not recognize the method , and this method cannot be translated into a store expression.

为什么啊？？？