Question

我有2个内连接（3个表），但我不知道，我发现很难在LINQ中实现关于外连接的研究。如何将最后一个内部联接更改为外部联接，以便即使列（Role）为null，该列仍将连接？

这是我想要转换为LINQ的现有SQL版本：

SELECT dbo.EmployeeAccess.id, dbo.EmployeeAccess.EmpNo, dbo.EmployeeAccess.RoleID, dbo.EmployeeAccess.Active, dbo.EmployeeAccessLevel.Role, 
                  dbo.View_HCM.LNameByFName

FROM  dbo.EmployeeAccess LEFT OUTER JOIN
      dbo.EmployeeAccessLevel ON dbo.EmployeeAccess.RoleID = dbo.EmployeeAccessLevel.id INNER JOIN
      dbo.View_HCM ON dbo.EmployeeAccess.EmpNo = dbo.View_HCM.EmpNo

LINQ我现在有2个内部联接：

    (from ea in context.EmployeeAccesses
                    join vh in context.View_HCM on (Int16)ea.EmpNo equals vh.EmpNo
                    join rl in context.EmployeeAccessLevels on ea.RoleID equals rl.id 
                    select new EmployeeWithEmail{

                        EmpNum = ea.EmpNo ?? 0,
                        EmailAddress = vh.EmailAddress,                          
                        LNameByFname = vh.LNameByFName,                                  
                        Active2 = ea.Active ?? false

                    }).ToList();
        }

Answer 1

Linq的外连接语法使用2部分。首先是into然后是DefaultIfEmpty

在您的情况下，外部联接可能如下所示：

(from ea in context.EmployeeAccesses
join vh in context.View_HCM on (Int16)ea.EmpNo equals vh.EmpNo
join rl in context.EmployeeAccessLevels on ea.RoleID equals rl.id into outer_join
from subjoin in outer_join.DefaultIfEmpty()
select new EmployeeWithEmail{

    EmpNum = ea.EmpNo ?? 0,
    EmailAddress = vh.EmailAddress,                          
    LNameByFname = vh.LNameByFName,                                  
    Active2 = ea.Active ?? false

}).ToList();

如何在LINQ中创建外部联接有many tutorials。

LINQ：内连接2表+外连接1表

1 个答案: