在Linq to SQL上是否可以实现干净的SQL?

在linq-to-sql中,是否可以实现干净的(或者我应该说是性能良好的)sql?

我希望Linq to SQL生成以下代码:

SELECT C.CustomerID, COUNT(O.CustomerID) AS N
FROM Customers C
LEFT JOIN Orders O ON O.CustomerID = C.CustomerID
GROUP BY C.CustomerID

我遵循以下准则: LINQ - Left Join, Group By, and Count

下面是我的代码版本:

var q = from c in db.Customers
        join o in db.Orders on c.CustomerID equals o.CustomerID into sr
        from x in sr.DefaultIfEmpty()
        group x by c.CustomerID into y
        select new { y.Key, N = y.Count(t => t.CustomerID != null) };

但它产生了这个…

SELECT [t2].[CustomerID] AS [Key], (
    SELECT COUNT(*)
    FROM [Customers] AS [t3]
    LEFT OUTER JOIN [Orders] AS [t4] ON [t3].[CustomerID] = [t4].[CustomerID]
    WHERE ([t4].[CustomerID] IS NOT NULL) AND ((([t2].[CustomerID] IS NULL) AND ([t3].[CustomerID] IS NULL)) OR (([t2].[CustomerID] IS NOT NULL) AND ([t3].[CustomerID] IS NOT NULL) AND ([t2].[CustomerID] = [t3].[CustomerID])))
    ) AS [N]
FROM (
    SELECT [t0].[CustomerID]
    FROM [Customers] AS [t0]
    LEFT OUTER JOIN [Orders] AS [t1] ON [t0].[CustomerID] = [t1].[CustomerID]
    GROUP BY [t0].[CustomerID]
    ) AS [t2]

…我觉得不可接受。

然后我试试这个…

var q = from c in db.Customers
        join o in db.Orders on c.CustomerID equals o.CustomerID into sr
        from x in sr.DefaultIfEmpty()
        group x by c.CustomerID into y                                        
        select new { y.Key, N = y.Sum(t => t.CustomerID != null ? 1 : 0 )};

…下面是结果查询:

SELECT SUM(
    (CASE
        WHEN [t1].[CustomerID] IS NOT NULL THEN @p0
        ELSE @p1
     END)) AS [N], [t0].[CustomerID] AS [Key]
FROM [Customers] AS [t0]
LEFT OUTER JOIN [Orders] AS [t1] ON [t0].[CustomerID] = [t1].[CustomerID]
GROUP BY [t0].[CustomerID]

虽然有点干净,看起来很有表现力,但与简单的陈述相比,还是没有那么简洁和表现力: COUNT(O.CustomerID)

在Linq to SQL中,我所要做的是可能的吗?

其他ORM呢?特别是nhibernate,它能将hql语句转换为真正的sql吗?