如何從一組有序的實體中查詢每個第n個值？

Question

我想查詢爲每第n行設置一個EF 4實體，以便得到不超過x個結果。例如，給定一組1000個名字，給我每100個名字（按課程名稱排序），以便我有10個結果。

LINQ to Entities可以以任何有效的方式實現這種事情嗎？

Answer 1

不在L2S，但你可以用ExecuteStoreQuery做到這一點：

你想SQL這樣的：

SELECT 
[Project1].[C1] AS [C1], 
[Project1].[DepartmentId] AS [DepartmentId], 
[Project1].[Code] AS [Code], 
[Project1].[DepartmentName] AS [DepartmentName] 
FROM (SELECT [Project1].[DepartmentId] AS [DepartmentId], [Project1].[Code] AS [Code], [Project1].[DepartmentName] AS [DepartmentName], [Project1].[C1] AS [C1], row_number() OVER (ORDER BY [Project1].[DepartmentName] ASC) AS [row_number] 
    FROM (SELECT 
     [Extent1].[DepartmentId] AS [DepartmentId], 
     [Extent1].[Code] AS [Code], 
     [Extent1].[DepartmentName] AS [DepartmentName] 
     1 AS [C1] 
     FROM [dbo].[Department] AS [Extent1] 
    ) AS [Project1] 
) AS [Project1] 
WHERE [Project1].[row_number] % 4 = 0   
ORDER BY [Project1].[DepartmentName] ASC 

（或替代一個參數有關我的硬編碼4）

而且然後代碼如下：

var q = Context.ExecuteStoreQuery<Foo>(
    sql, params);