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VS 2008 sp1 + .NET 3.5 sp1(3)

編輯：關於.NET

Entity Framework(實體框架)之詳解 Linq To Entities 之二

介紹

以Northwind為示例數據庫，ADO.NET Entity Framework之Linq To Entities

Select - 選擇需要返回的字段

Where - 篩選

OrderBy - 正序排序

OrderByDescending - 倒序排序

ThenBy - 在 OrderBy 或 OrderByDescending 的基礎上再正序排序

ThenByDescending - 在 OrderBy 或 OrderByDescending 的基礎上再倒序排序

GroupBy - 分組

Join - 連接

GroupJoin - 連接後分組

示例

Select

using (var ctx = new NorthwindEntities())
{
　　// Select 對應的 Linq 方法
　　var p1 = ctx.Products.Select(p => new { ProductName = "產品名稱：" + p.ProductName 

});
　　p1.ToList();
　　
　　// Select 對應的查詢語法
　　var p2 = from p in ctx.Products select new { ProductName = "產品名稱：" + p.ProductName 

};
　　p2.ToList();
}
--Select 對應的 sql 語句
　　
SELECT
1 AS [C1],
N'產品名稱：' + [Extent1].[ProductName] AS [C2]
FROM [dbo].[Products] AS [Extent1]

Where

using (var ctx = new NorthwindEntities())
{
　　// Where 對應的 Linq 方法
　　var p1 = ctx.Products.Where(p => p.ProductID > 3);
　　p1.ToList();
　　
　　// Where 對應的查詢語法
　　var p2 = from p in ctx.Products where p.ProductID > 3 select p;
　　p2.ToList();
}
--Where 對應的 sql 語句
　　
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 對應的 Linq 方法
　　var p1 = ctx.Products.OrderBy(p => p.UnitPrice);
　　p1.ToList();
　　
　　// OrderBy 對應的查詢語法
　　var p2 = from p in ctx.Products orderby p.UnitPrice select p;
　　p2.ToList();
}
--OrderBy 對應的 sql 語句
　　
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 對應的 Linq 方法
　　var p1 = ctx.Products.OrderByDescending(p => p.UnitPrice);
　　p1.ToList();
　　
　　// OrderByDescending 對應的查詢語法
　　var p2 = from p in ctx.Products orderby p.UnitPrice descending select p;
　　p2.ToList();
}
--OrderByDescending 對應的 sql 語句
　　
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 對應的 Linq 方法
　　var p1 = ctx.Products.OrderBy(p => p.UnitPrice).ThenBy(p => p.ProductID);
　　p1.ToList();
　　
　　// ThenBy 對應的查詢語法
　　var p2 = from p in ctx.Products orderby p.UnitPrice ascending, p.ProductID ascending 

select p;
　　p2.ToList();
}
--ThenBy 對應的 sql 語句
　　
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 對應的 Linq 方法
　　var p1 = ctx.Products.OrderBy(p => p.UnitPrice).ThenByDescending(p => 

p.ProductID);
　　p1.ToList();
　　
　　// ThenByDescending 對應的查詢語法
　　var p2 = from p in ctx.Products orderby p.UnitPrice ascending, p.ProductID descending 

select p;
　　p2.ToList();
}
--ThenByDescending 對應的 sql 語句
　　
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 對應的 Linq 方法
　　var p1 = ctx.Products.GroupBy(p => p.Suppliers.SupplierID).Select(g => new { Group 

= g.Key, Member = g });
　　foreach (var g in p1)
　　{
　　　　// g.Group - 供貨商ID，以此分組
　　　　// g.Member - 某供貨商下的所有產品
　　　　foreach (var m in g.Member)
　　　　{
　　　　　　// code
　　　　}
　　}
　　
　　// GroupBy 對應的查詢語法
　　var p2 = from p in ctx.Products group p by p.Suppliers.SupplierID into g select new { 

Group = g.Key, Member = g };
　　foreach (var g in p2)
　　{
　　　　// g.Group - 供貨商ID，以此分組
　　　　// g.Member - 某供貨商下的所有產品
　　　　foreach (var m in g.Member)
　　　　{
　　　　　　// code
　　　　}
　　}
}
--GroupBy 對應的 sql 語句
　　
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 對應的 Linq 方法
　　var p1 = ctx.Products.Join(
　　　　ctx.Categories,
　　　　p => p.Categories.CategoryID,
　　　　c => c.CategoryID,
　　　　(p, c) => new { c.CategoryName, p.ProductName });
　　p1.ToList();
　　
　　// Join 對應的查詢語法
　　var p2 = from p in ctx.Products
　　　　　　 join c in ctx.Categories
　　　　　　 on p.Categories.CategoryID equals c.CategoryID
　　　　　　 select new { c.CategoryName, p.ProductName };
　　p2.ToList();
}
--Join 對應的 sql 語句
　　
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 對應的 Linq 方法
　　var p1 = ctx.Categories.GroupJoin(
　　　　ctx.Products,
　　　　c => c.CategoryID,
　　　　p => p.Categories.CategoryID,
　　　　(p, g) => new { p.CategoryName, ProductCount = g.Count() });
　　p1.ToList();
　　
　　// GroupJoin 對應的查詢語法
　　var p2 = from c in ctx.Categories
　　　　　　 join p in ctx.Products
　　　　　　 on c.CategoryID equals p.Categories.CategoryID into g // g - 

IEnumerable<Products>
　　　　　　 select new { CategoryName = c.CategoryName, ProductCount = g.Count() };
　　p2.ToList();
}
--GroupJoin 對應的 sql 語句
　　
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]