再接再厉VS 2008 sp1 + .NET 3.5 sp1(3) - Entity Framework(实体框架)之详解 Linq To Entities 之二

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再接再厉VS 2008 sp1 + .NET 3.5 sp1(3) - Entity Framework(实体框架)之详解 Linq To Entities 之二

作者： webabcd


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 Linq 方法
        var p1 = ctx.Products. Select(p => new { ProductName = "产品名称：" + p.ProductName });
        p1.ToList();

        // Select 对应的查询语法
        var p2 = from p in ctx.Products select new { ProductName = "产品名称：" + p.ProductName };
        p2.ToList();
}
-- 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 Linq 方法
        var p1 = ctx.Products.Where(p => p.ProductID > 3);
        p1.ToList();

        // Where 对应的查询语法
        var p2 = from p in ctx.Products where p.ProductID > 3 select p;
        p2.ToList();
}
--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 Linq 方法
        var p1 = ctx.Products.OrderBy(p => p.UnitPrice);
        p1.ToList();

        // OrderBy 对应的查询语法
        var p2 = from p in ctx.Products orderby p.UnitPrice select p;
        p2.ToList();
}
--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 Linq 方法
        var p1 = ctx.Products.OrderByDescending(p => p.UnitPrice);
        p1.ToList();

        // OrderByDescending 对应的查询语法
        var p2 = from p in ctx.Products orderby p.UnitPrice descending select p;
        p2.ToList();
}
--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 Linq 方法
        var p1 = ctx.Products.OrderBy(p => p.UnitPrice).ThenBy(p => p.ProductID);
        p1.ToList();

        // ThenBy 对应的查询语法
        var p2 = from p in ctx.Products orderby p.UnitPrice ascending, p.ProductID ascending select p;
        p2.ToList();
}
--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 Linq 方法
        var p1 = ctx.Products.OrderBy(p => p.UnitPrice).ThenByDescending(p => p.ProductID);
        p1.ToList();

        // ThenByDescending 对应的查询语法
        var p2 = from p in ctx.Products orderby p.UnitPrice ascending, p.ProductID descending select p;
        p2.ToList();
}
--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 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 - 供货商ID，以此分组
                // g.Member - 某供货商下的所有产品
                foreach (var m in g.Member)
                {
                        // code
                }
        }

        // GroupBy 对应的查询语法
        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 - 供货商ID，以此分组
                // g.Member - 某供货商下的所有产品
                foreach (var m in g.Member)
                {
                        // code
                }
        }
}
--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 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 对应的查询语法
        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 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 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 对应的查询语法
        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 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]

 

 

OK
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