CLR Table-Valued函数

这几天来，努力学习了CLR的存储过程，创建与部署。从普通的存储过程，带参数，以及Output返回值等。Insus.NET今天学习一个例子，怎样实现CLR Table-Valued函数。在数据库中，我们可以看到很多种函数类型，Table-falued function,Scalar-valued function 等等。

这篇练习的CLR中编写的函数就是table-valued function。

在VS开发SQL的 CLR程序，有简单有复杂，看开发时的衡量了。有些在SQL中无法实现的，可以写成CLR，然后再部署至SQL中。此篇并没有看出两者之间的优势，仅是一个例子作为参考。比如我们想创建一个多表查询LEFT JOIN。把SQL语句写成一个table-valued函数。这个多表查询，所返回的字段，定义成一个类别：上面代码示例，可复制代码:

using System;using System.Collections.Generic;using System.Data;using System.Data.SqlTypes;using System.Text;namespace Insus.NET{    class Fruit    {        public byte Fruit_nbr { get; set; }        public byte  FruitCategory_nbr { get; set; }        public string CategoryName { get; set; }        public byte FruitKind_nbr { get; set; }        public string  KindName { get; set; }        public string  FruitName { get; set; }    }}

创建一个新Item: 按下面的步骤，在标记5中选择SQL CLR C# User Defined Function。

标记6,给一个名字，标记7"Add"之后：

删除#14至#19行代码，添加下面代码：

上面代码示例，可复杂代码：

using System;using System.Data;using System.Data.SqlClient;using System.Data.SqlTypes;using Microsoft.SqlServer.Server;using System.Collections;using Insus.NET;using System.Collections.Generic;public partial class UserDefinedFunctions{    [SqlFunction(Dataaccess = DataAccessKind.Read,                 FillRowMethodName = "Item_FillRow",                 TableDefinition = "Fruit_nbr TINYINT,FruitCategory_nbr TINYINT, " +                                  "CategoryName NVARCHAR(30),FruitKind_nbr TINYINT," +                                  "KindName NVARCHAR(30),FruitName NVARCHAR(30)"                 )    ]    public static IEnumerable Tvf_Fruit()    {        List<Fruit> fruitConnections = new List<Fruit>();        using (SqlConnection connection = new SqlConnection("context connection=true"))        {            connection.Open();            string sql = "SELECT [Fruit_nbr],[FruitCategory_nbr],[CategoryName]," +                "u_fk.[FruitKind_nbr],[KindName],[FruitName] FROM [dbo].[Fruit] AS f " +                "LEFT JOIN [dbo].[udf_FruitKind]() AS u_fk ON (f.[FruitKind_nbr] = u_fk.[FruitKind_nbr])";            using (SqlCommand command = new SqlCommand(sql, connection))            {                using (SqlDataReader objDr = command.ExecuteReader())                {                    while (objDr.Read())                    {                        Fruit oFruit = new Insus.NET.Fruit();                        oFruit.Fruit_nbr = (byte)objDr["Fruit_nbr"];                        oFruit.FruitCategory_nbr = (byte)objDr["FruitCategory_nbr"];                        oFruit.CategoryName = objDr["CategoryName"].ToString();                        oFruit.FruitKind_nbr = (byte)objDr["FruitKind_nbr"];                        oFruit.KindName = objDr["KindName"].ToString();                        oFruit.FruitName = objDr["FruitName"].ToString();                        fruitConnections.Add(oFruit);                    }                }            }        }        return fruitConnections;    }    PRivate static void Item_FillRow(object source, out SqlByte fruit_nbr,        out SqlByte fruitCategory_nbr, out SqlChars categoryName,        out SqlByte fruitKind_nbr, out SqlChars kindName, out SqlChars fruitName)    {        Fruit fruit = (Fruit)source;        fruit_nbr = new SqlByte(fruit.Fruit_nbr);        fruitCategory_nbr = new SqlByte(fruit.FruitCategory_nbr);        categoryName = new SqlChars(fruit.CategoryName);        fruitKind_nbr = new SqlByte(fruit.FruitKind_nbr);        kindName = new SqlChars(fruit.KindName);        fruitName = new SqlChars(fruit.FruitName);    }}

接下来，Build，然后可以部署至SQL中去。上面可复制代码：

IF EXISTS (SELECT * FROM sys.objects WHERE name = 'Tvf_Fruit')    DROP FUNCTION Tvf_Fruit;GOIF EXISTS (SELECT * FROM sys.assemblies WHERE name = 'FruitClr')    DROP ASSEMBLY FruitClr;GOCREATE ASSEMBLY FruitClrFROM 'E:/FruitClr.dll' WITH PERMISSION_SET = SAFE;GOCREATE FUNCTION Tvf_Fruit()RETURNS TABLE (    Fruit_nbr TINYINT,    FruitCategory_nbr TINYINT,    CategoryName NVARCHAR(30),    FruitKind_nbr TINYINT,    KindName NVARCHAR(30),    FruitName NVARCHAR(30))ASEXTERNAL NAME [FruitClr].UserDefinedFunctions.Tvf_Fruit;GO

执行成功之后，你肯定会发现SQL发生变化的两个位置：

此时table-valued function创建成功了，在查询分析器执行一下Tvf_Fruit()函数。

下面内容于2015-03-31 09:30分添加：看看执行的效率如何？ 标记1是原始写法，标记2是写成Clr函数。它们得到结果是一样的。