Linq to sql - 生成错误的sql？

Question

我有带有表 Employee、Phone 和 Email 的 SQL 2008 服务器，其中 Employee 与 Phone 和 Email 是一对多的关系（因此员工可以有很多电话号码和电子邮件）。

现在我想用所有电话和电子邮件查询员工：

var query = (from e in db.Employee select new EmployeeDTO { Id = e.Id, Name = e.Name, Phones = e.Phones, Emails = e.Emails }).ToList();

但是 linq 将其转换为非常丑陋的 sql，它使用电话表进行左连接，但随后在单独的查询中查询每个员工的电子邮件，例如：

SELECT [t0].[EmployeeID], [t0].[Name], [t1].[Phone] (
    SELECT COUNT(*)
    FROM [dbo].[Phone] AS [t2]
    WHERE [t2].[EmployeeID] = [t0].[EmployeeID]
    ) AS [value]
FROM [dbo].[Employee] AS [t0]
LEFT OUTER JOIN [dbo].[Phone] AS [t1] ON [t1].[EmployeeID] = [t0].[EmployeeID]
ORDER BY [t0].[EmployeeID], [t1].[PhoneID]
-- Context: SqlProvider(Sql2008) Model: AttributedMetaModel Build: 3.5.30729.4926

SELECT [t0].[EmailID], [t0].[Email]
FROM [dbo].[Email] AS [t0]
WHERE [t0].[EmployeeID] = @x1
-- @x1: Input UniqueIdentifier (Size = 0; Prec = 0; Scale = 0) [1ed2e9a0-ca4b-4912-8f8e-000ed8d0b2af]
-- Context: SqlProvider(Sql2008) Model: AttributedMetaModel Build: 3.5.30729.4926

SELECT [t0].[EmailID], [t0].[Email]
FROM [dbo].[Email] AS [t0]
WHERE [t0].[EmployeeID]= @x1
-- @x1: Input UniqueIdentifier (Size = 0; Prec = 0; Scale = 0) [2203192b-05ef-4b59-b4b4-0010e26a8119]
-- Context: SqlProvider(Sql2008) Model: AttributedMetaModel Build: 3.5.30729.4926

我需要的是简单的sql：

SELECT [t0].[EmployeeID], [t0].[Name], [t1].[Phone], [t2].[Email]
FROM [dbo].[Employee] AS [t0]
LEFT OUTER JOIN [dbo].[Phone] AS [t1] ON [t1].[EmployeeID] = [t0].[EmployeeID]
LEFT OUTER JOIN [dbo].[Email] AS [t2] ON [t2].[EmployeeID] = [t0].[EmployeeID]

如何在不对结果进行分组的情况下编写这样的 linq 查询？ 我知道如何进行多个左连接，但是我需要按 EmployeeID 对结果进行分组。

Answer 1

你试过这样做吗？

var query = (from e in db.Employee
    join p in db.Phones on e.EmployeeID equals p.EmployeeID into tmpPhones
    from phones in tmpPhones.DefaultIfEmpty()
    join m in db.Emails on e.EmployeeID equals m.EmployeeID into tmpEmails
    from emails in tmpEmails.DefaultIfEmpty()

             select new EmployeeDTO
             {
                 Id = e.Id,
                 Name = e.Name,
                 Phones = phones,
                 Emails = emails
             }).ToList();

您需要的是 LoadWith 来处理多个一对多关系，但这不起作用 -

http://social.msdn.microsoft.com/forums/en-US/linqprojectgeneral/thread/a68744f6-e1f3-4d28-82eb-87b8187ec0a8/

跳圈应该可行 -

 var query = (from e in db.Employee
        join p in db.Phones on e.EmployeeID equals p.EmployeeID into tmpPhones
        from phones in tmpPhones.DefaultIfEmpty()
        join m in db.Emails on e.EmployeeID equals m.EmployeeID into tmpEmails
        from emails in tmpEmails.DefaultIfEmpty()
        group e by e into eGrp

                 select new EmployeeDTO
                 {
                     Id = eGrp.Key.Id,
                     Name = eGrp.Key.Name,
                     Phones = eGrp.Select(x => x.Phones),
                     Emails = eGrp.Select(x => x.Emails)
                 }).ToList();