Entity Framework(实体框架)之详解 Linq To Entities 之二(转载)

介绍
以Northwind为示例数据库，ADO.NET Entity Framework之Linq To Entities

Select - 选择需要返回的字段
Where - 筛选
OrderBy - 正序排序
OrderByDescending - 倒序排序
ThenBy - 在 OrderBy 或 OrderByDescending 的基础上再正序排序
ThenByDescending - 在 OrderBy 或 OrderByDescending 的基础上再倒序排序
GroupBy - 分组
Join - 连接
GroupJoin - 连接后分组

示例
Select

using (var ctx = new NorthwindEntities())
--Select 对应的 sql 语句

SELECT
1 AS [C1],
N'产品名称：' + [Extent1].[ProductName] AS [C2]
FROM [dbo].[Products] AS [Extent1]
Where

using (var ctx = new NorthwindEntities())
--Where 对应的 sql 语句

SELECT
1 AS [C1],
[Extent1].[Discontinued] AS [Discontinued],
[Extent1].[ProductID] AS [ProductID],
[Extent1].[ProductName] AS [ProductName],
[Extent1].[QuantityPerUnit] AS [QuantityPerUnit],
[Extent1].[ReorderLevel] AS [ReorderLevel],
[Extent1].[UnitPrice] AS [UnitPrice],
[Extent1].[UnitsInStock] AS [UnitsInStock],
[Extent1].[UnitsOnOrder] AS [UnitsOnOrder],
[Extent1].[CategoryID] AS [CategoryID],
[Extent1].[SupplierID] AS [SupplierID]
FROM [dbo].[Products] AS [Extent1]
WHERE [Extent1].[ProductID] > 3
OrderBy

using (var ctx = new NorthwindEntities())
--OrderBy 对应的 sql 语句

SELECT
[Project1].[C1] AS [C1],
[Project1].[Discontinued] AS [Discontinued],
[Project1].[ProductID] AS [ProductID],
[Project1].[ProductName] AS [ProductName],
[Project1].[QuantityPerUnit] AS [QuantityPerUnit],
[Project1].[ReorderLevel] AS [ReorderLevel],
[Project1].[UnitPrice] AS [UnitPrice],
[Project1].[UnitsInStock] AS [UnitsInStock],
[Project1].[UnitsOnOrder] AS [UnitsOnOrder],
[Project1].[CategoryID] AS [CategoryID],
[Project1].[SupplierID] AS [SupplierID]
FROM ( SELECT
[Extent1].[CategoryID] AS [CategoryID],
[Extent1].[Discontinued] AS [Discontinued],
[Extent1].[ProductID] AS [ProductID],
[Extent1].[ProductName] AS [ProductName],
[Extent1].[QuantityPerUnit] AS [QuantityPerUnit],
[Extent1].[ReorderLevel] AS [ReorderLevel],
[Extent1].[SupplierID] AS [SupplierID],
[Extent1].[UnitPrice] AS [UnitPrice],
[Extent1].[UnitsInStock] AS [UnitsInStock],
[Extent1].[UnitsOnOrder] AS [UnitsOnOrder],
1 AS [C1]
FROM [dbo].[Products] AS [Extent1]
) AS [Project1]
ORDER BY [Project1].[UnitPrice] ASC
OrderByDescending

using (var ctx = new NorthwindEntities())
--OrderByDescending 对应的 sql 语句

SELECT
[Project1].[C1] AS [C1],
[Project1].[Discontinued] AS [Discontinued],
[Project1].[ProductID] AS [ProductID],
[Project1].[ProductName] AS [ProductName],
[Project1].[QuantityPerUnit] AS [QuantityPerUnit],
[Project1].[ReorderLevel] AS [ReorderLevel],
[Project1].[UnitPrice] AS [UnitPrice],
[Project1].[UnitsInStock] AS [UnitsInStock],
[Project1].[UnitsOnOrder] AS [UnitsOnOrder],
[Project1].[CategoryID] AS [CategoryID],
[Project1].[SupplierID] AS [SupplierID]
FROM ( SELECT
[Extent1].[CategoryID] AS [CategoryID],
[Extent1].[Discontinued] AS [Discontinued],
[Extent1].[ProductID] AS [ProductID],
[Extent1].[ProductName] AS [ProductName],
[Extent1].[QuantityPerUnit] AS [QuantityPerUnit],
[Extent1].[ReorderLevel] AS [ReorderLevel],
[Extent1].[SupplierID] AS [SupplierID],
[Extent1].[UnitPrice] AS [UnitPrice],
[Extent1].[UnitsInStock] AS [UnitsInStock],
[Extent1].[UnitsOnOrder] AS [UnitsOnOrder],
1 AS [C1]
FROM [dbo].[Products] AS [Extent1]
) AS [Project1]
ORDER BY [Project1].[UnitPrice] DESC
ThenBy

using (var ctx = new NorthwindEntities())
--ThenBy 对应的 sql 语句

SELECT
[Project1].[C1] AS [C1],
[Project1].[Discontinued] AS [Discontinued],
[Project1].[ProductID] AS [ProductID],
[Project1].[ProductName] AS [ProductName],
[Project1].[QuantityPerUnit] AS [QuantityPerUnit],
[Project1].[ReorderLevel] AS [ReorderLevel],
[Project1].[UnitPrice] AS [UnitPrice],
[Project1].[UnitsInStock] AS [UnitsInStock],
[Project1].[UnitsOnOrder] AS [UnitsOnOrder],
[Project1].[CategoryID] AS [CategoryID],
[Project1].[SupplierID] AS [SupplierID]
FROM ( SELECT
[Extent1].[CategoryID] AS [CategoryID],
[Extent1].[Discontinued] AS [Discontinued],
[Extent1].[ProductID] AS [ProductID],
[Extent1].[ProductName] AS [ProductName],
[Extent1].[QuantityPerUnit] AS [QuantityPerUnit],
[Extent1].[ReorderLevel] AS [ReorderLevel],
[Extent1].[SupplierID] AS [SupplierID],
[Extent1].[UnitPrice] AS [UnitPrice],
[Extent1].[UnitsInStock] AS [UnitsInStock],
[Extent1].[UnitsOnOrder] AS [UnitsOnOrder],
1 AS [C1]
FROM [dbo].[Products] AS [Extent1]
) AS [Project1]
ORDER BY [Project1].[UnitPrice] ASC, [Project1].[ProductID] ASC
ThenByDescending

using (var ctx = new NorthwindEntities())
--ThenByDescending 对应的 sql 语句

SELECT
[Project1].[C1] AS [C1],
[Project1].[Discontinued] AS [Discontinued],
[Project1].[ProductID] AS [ProductID],
[Project1].[ProductName] AS [ProductName],
[Project1].[QuantityPerUnit] AS [QuantityPerUnit],
[Project1].[ReorderLevel] AS [ReorderLevel],
[Project1].[UnitPrice] AS [UnitPrice],
[Project1].[UnitsInStock] AS [UnitsInStock],
[Project1].[UnitsOnOrder] AS [UnitsOnOrder],
[Project1].[CategoryID] AS [CategoryID],
[Project1].[SupplierID] AS [SupplierID]
FROM ( SELECT
[Extent1].[CategoryID] AS [CategoryID],
[Extent1].[Discontinued] AS [Discontinued],
[Extent1].[ProductID] AS [ProductID],
[Extent1].[ProductName] AS [ProductName],
[Extent1].[QuantityPerUnit] AS [QuantityPerUnit],
[Extent1].[ReorderLevel] AS [ReorderLevel],
[Extent1].[SupplierID] AS [SupplierID],
[Extent1].[UnitPrice] AS [UnitPrice],
[Extent1].[UnitsInStock] AS [UnitsInStock],
[Extent1].[UnitsOnOrder] AS [UnitsOnOrder],
1 AS [C1]
FROM [dbo].[Products] AS [Extent1]
) AS [Project1]
ORDER BY [Project1].[UnitPrice] ASC, [Project1].[ProductID] DESC
GroupBy

using (var ctx = new NorthwindEntities())
--GroupBy 对应的 sql 语句

SELECT
[Project2].[SupplierID] AS [SupplierID],
[Project2].[C1] AS [C1],
[Project2].[C2] AS [C2],
[Project2].[C4] AS [C3],
[Project2].[C3] AS [C4],
[Project2].[Discontinued] AS [Discontinued],
[Project2].[ProductID] AS [ProductID],
[Project2].[ProductName] AS [ProductName],
[Project2].[QuantityPerUnit] AS [QuantityPerUnit],
[Project2].[ReorderLevel] AS [ReorderLevel],
[Project2].[UnitPrice] AS [UnitPrice],
[Project2].[UnitsInStock] AS [UnitsInStock],
[Project2].[UnitsOnOrder] AS [UnitsOnOrder],
[Project2].[CategoryID] AS [CategoryID],
[Project2].[SupplierID1] AS [SupplierID1]
FROM ( SELECT
[Distinct1].[SupplierID] AS [SupplierID],
1 AS [C1],
1 AS [C2],
CASE WHEN ([Extent2].[Discontinued] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C3],
[Extent2].[CategoryID] AS [CategoryID],
[Extent2].[Discontinued] AS [Discontinued],
[Extent2].[ProductID] AS [ProductID],
[Extent2].[ProductName] AS [ProductName],
[Extent2].[QuantityPerUnit] AS [QuantityPerUnit],
[Extent2].[ReorderLevel] AS [ReorderLevel],
[Extent2].[SupplierID] AS [SupplierID1],
[Extent2].[UnitPrice] AS [UnitPrice],
[Extent2].[UnitsInStock] AS [UnitsInStock],
[Extent2].[UnitsOnOrder] AS [UnitsOnOrder],
CASE WHEN ([Extent2].[Discontinued] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C4]
FROM (SELECT DISTINCT
[Extent1].[SupplierID] AS [SupplierID]
FROM [dbo].[Products] AS [Extent1] ) AS [Distinct1]
LEFT OUTER JOIN [dbo].[Products] AS [Extent2] ON ([Extent2].[SupplierID] = [Distinct1].[SupplierID]) OR (([Extent2].[SupplierID] IS NULL) AND ([Distinct1].[SupplierID] IS NULL))
) AS [Project2]
ORDER BY [Project2].[SupplierID] ASC, [Project2].[C4] ASC
Join

using (var ctx = new NorthwindEntities())
--Join 对应的 sql 语句

SELECT
1 AS [C1],
[Extent2].[CategoryName] AS [CategoryName],
[Extent1].[ProductName] AS [ProductName]
FROM [dbo].[Products] AS [Extent1]
INNER JOIN [dbo].[Categories] AS [Extent2] ON ([Extent1].[CategoryID] = [Extent2].[CategoryID]) OR (([Extent1].[CategoryID] IS NULL) AND ([Extent2].[CategoryID] IS NULL))
GroupJoin

using (var ctx = new NorthwindEntities())
--GroupJoin 对应的 sql 语句

SELECT
1 AS [C1],
[Project1].[CategoryName] AS [CategoryName],
[Project1].[C1] AS [C2]
FROM ( SELECT
[Extent1].[CategoryName] AS [CategoryName],
(SELECT
COUNT(cast(1 as bit)) AS [A1]
FROM [dbo].[Products] AS [Extent2]
WHERE ([Extent1].[CategoryID] = [Extent2].[CategoryID]) OR (([Extent1].[CategoryID] IS NULL) AND ([Extent2].[CategoryID] IS NULL))) AS [C1]
FROM [dbo].[Categories] AS [Extent1]
) AS [Project1]