关于linq to entity Left join 的问题
select * from [table1] a
left join [table2] b on a.ID = b.ID
left join [table3] c on a.ID = c.ID
left join [table4] c on a.ID = c.ID
.....
...

如何转换成LinQ啊...

貌似用了Linqer也没用

[最优解释]
from c in table1
join p in table2 on c.ID equals p.PID into t1
from p in t1.DefaultIfEmpty()
join d in table3 on p.EID equals pi.PIID into t2
from d in t2.DefalutIfEmpty()
select c;
[其他解释]

from c in table1
join p in table2 on c.ID equals p.PID           
join d in table3 on p.EID equals pi.PIID     
select new
{
    c.ID, p.PID, pi.PIID
}

[其他解释]

引用:

C# code123456789from c in table1join p in table2 on c.ID equals p.PID join d in table3 on p.EID equals pi.PIID select new{ c.ID, p.PID, pi.PIID}

0. 0其实看得不是很懂..
[Table1]中的ID包含了其他所有表中的ID并且其他表中的ID是不相同的
这种情况下光是用join进行多表联合查不到数据...
[其他解释]

引用:

from c in table1
join p in table2 on c.ID equals p.PID into t1
from p in t1.DefaultIfEmpty()
join d in table3 on p.EID equals pi.PIID into t2
from d in t2.DefalutIfEmpty()
……

..我用这种方法结果是
base {System.SystemException} = {"到值类型“Guid”的强制转换失败，因为具体化值为 null。结果类型的泛型参数或查询必须使用可以为 null 的类型。"}

我的LINQ是这样写的

var result = (from a in table1
           join b in table2 on a.a_guid equals b.b_guid into t1
           from b in t1.DefaultIfEmpty()
           join c in table3 on a.a_guid equals c.c_guid into t2
           from c in t2.DefaultIfEmpty()
           join e in table4 on a.a_userid equals e.e_userid into t3
           from e in t3.DefaultIfEmpty()
           orderby a.CreateWhen
select new {....});

------其他解决方案--------------------

=. =好吧我知道了 因为 当table2 有值的时候 table3 必然是空的..反之同理..
当遇到这种情况的时候应该肿么解决呢
[其他解释]
帖出你的select new里的代码
[其他解释]
0. 0 貌似我是解决了

 select new
                              {
                                  a,
                                  b,
                                  c,
                                  e
                                  //DynamicGUID = a.DynamicGUID,
                                  //DynamicType = a.DynamicType,
                                  //CreateWhen = a.CreateWhen,
                                  //UserID = e.UserID,
                                  //UserGUID = e.UserGUID,
                                  //Avatar = e.Avatar,
                                  //Name = e.Name,
                                  //Body = b.Body,
                                  //SimpleCategory = c.SimpleCategory,
                                  //IndustryCategory = c.IndustryCategory,
                                  //AreaCategory = c.AreaCategory, 
 
                                  //JobCategory = c.JobCategory,
                                  //DepartmentCategory = c.DepartmentCategory,
                                  //BusinessDescription = c.BusinessDescription
                              });

之前select的是注释了的东西..现在直接select a b c e..然后foreach 用 item.a/b/c/e ...
这样=. = 好像可以了
[其他解释]
你要理解原因
比如这句：
UserID = e.UserID,
因为e有可能为NULL，所以要这么写：
UserID =e==null?0:e.UserID,
才不会报错
[其他解释]

引用:

你要理解原因
比如这句：
UserID = e.UserID,
因为e有可能为NULL，所以要这么写：
UserID =e==null?0:e.UserID,
才不会报错

0. 0嗯....谢谢指教~~