左外连接Linq to Entities/SQL

如何在LINQ to Entities中编写以下SQL？左外连接Linq to Entities/SQL

SELECT r.rolename, 
     (CASE 
      WHEN ur.username IS NULL THEN 0 
      ELSE 1 
     END) AS isinrole 
FROM bgt.roles r 
     LEFT OUTER JOIN bgt.usersinroles ur 
     ON ur.rolename = r.rolename 
      AND ur.username = 'ADMIN'

来源

2011-06-12 Harindaka

变种查询=从r 加入乌尔在UsersInRoles上新{F1 = r.Rolename，F2 = 'ADMIN'} 等于新的{ f1 = ur.Rolename，f2 = ur.Username}从temp.DefaultIfEmpty（）中输入temp （） select new {f1 = r.RoleName，f2 = x.Username}; – Harindaka 2011-06-12 12:35:18

我听说EF中不支持DefaultIfEmpty。这是真的吗？ – Harindaka 2011-06-12 12:36:10

自EF 4.0开始支持DefaultIfEmpty' – 2011-06-12 13:28:37

这对我有用。感谢所有的建议。

var query = 
from r in Roles 
from ur in UsersInRoles 
.Where(v => v.Rolename == r.Rolename && v.Username == "ADMIN") 
.DefaultIfEmpty() 
select new { Rolename = r.Rolename, IsInRole = (ur.Username != null) };

生成的SQL是如在角色如下

SELECT 
1 AS [C1], 
[Extent1].[Rolename] AS [Rolename], 
CASE WHEN ([Extent2].[Username] IS NOT NULL) THEN cast(1 as bit) WHEN ([Extent2].[Username] IS NULL) THEN cast(0 as bit) END AS [C2] 
FROM [bgt].[Roles] AS [Extent1] 
LEFT OUTER JOIN [bgt].[UsersInRoles] AS [Extent2] ON ([Extent2].[Rolename] = [Extent1].[Rolename]) AND ('ADMIN' = [Extent2].[Username])

来源

2011-06-13 04:13:04 Harindaka

我会做这样的：

from role in db.Roles 
let isInRole = role.UsersInRoles.Any(u => u.UserName == "ADMIN") 
select new { role.RoleName, isInRole }

Althought生成的SQL是不是一样好你的。

来源

2011-06-12 12:54:55 svick

谢谢你让我朝正确的方向发展。以下为解决方案。 – Harindaka 2011-06-14 14:23:54

左外连接Linq to Entities/SQL

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