vs2008 linq2sql继续挖掘bug：表达式列支持问题

闲来无事...

使用Adventureworks数据库测试了linq2sql，发现其对表达式列支持不好，测试代码如下：

AdventureWorksDataContext db = new AdventureWorksDataContext();

Customer c = new Customer();

c.ModifiedDate = DateTime.Now;

c.rowguid = Guid.NewGuid();

c.TerritoryID = 1;

c.CustomerType = 'S';

//c.AccountNumber = "AW00000199";

db.Customers.Add(c);

db.SubmitChanges();

AccountNumber为表达式列，结果运行的时候抛出异常。

同时，发现其分页算法效率有点低，代码如下：
AdventureWorksDataContext db = new AdventureWorksDataContext();

var c = db.Customers.Skip(100).Take(100);

/*SELECT TOP 100 [t1].[CustomerID], [t1].[TerritoryID], [t1].[AccountNumber], [t1].[CustomerType], [t1].[rowguid], [t1].[ModifiedDate]

FROM (

SELECT ROW_NUMBER() OVER (ORDER BY [t0].[CustomerID], [t0].[TerritoryID], [t0].[AccountNumber], [t0].[CustomerType], [t0].[rowguid], [t0].[ModifiedDate]) AS [ROW_NUMBER], [t0].[CustomerID], [t0].[TerritoryID], [t0].[AccountNumber], [t0].[CustomerType], [t0].[rowguid], [t0].[ModifiedDate]

FROM [Sales].[Customer] AS [t0]

) AS [t1]

WHERE [t1].[ROW_NUMBER] > 100*/

使用Sql Server Query Visualizer可以看到上面的sql代码。其Row_Number() over了全部的列, 我在Management Studio中运行的时候上面的sql代码大概花费了40毫秒（前后加上Select getdate()），而如果Row_Number 只over主键CustomerID的话，则没看到时间差距。