再接再厉VS 2008 sp1 + .NET 3.5 sp1(4) - Entity Framework(实体框架)之EntityClient, ObjectQuery

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再接再厉VS 2008 sp1 + .NET 3.5 sp1(4) - Entity Framework(实体框架)之EntityClient, ObjectQuery

作者： webabcd


介绍
以Northwind为示例数据库，ADO.NET Entity Framework之详解EntityClient, ObjectQuery

• EntityConnection - 与存储模型的连接
• EntityCommand - 对 EDM 执行的命令
• EntityParameter - 配置 EntityCommand 的参数
• EntityDataReader - 以只读、只进的数据流的方式获取数据（内存中始终只有一行）。相当于SqlDataReader
• ObjectQuery<T> - 通过 Entity SQL 或 查询语法 或 Linq 方法对概念模型做查询
• ObjectContext.CreateQuery<T>(Entity SQL) - 根据 esql 创建一个 ObjectQuery<T> 。（延迟）

示例
1、关于EntityClient
EntityClient.aspx.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

using System.Data.Objects;
using System.Data.Objects.DataClasses;
using System.Data.EntityClient;
using System.Data;

using VS2008SP1.Business;

public partial class EntityFramework_EntityClient : System.Web.UI.Page
{
void Page_Load() void Page_Load(object sender, EventArgs e)
        {
                 if (!Page.IsPostBack)
                {
                        Demo();

                        result.InnerHtml += "<br />";

                        Demo2();

                        result.InnerHtml += "<br />";

                        Demo3();
                }
        }

        void Demo()
        {
                 string strConn = System.Configuration.ConfigurationManager.ConnectionStrings[ "NorthwindEntities"].ConnectionString;
                // EntityConnection - 与存储模型的连接。构造函数的参数为连接字符串
                //         Open() - 打开连接
                //         Close() - 关闭连接
                //         CreateCommand() - 创建此连接的 EntityCommand 对象
                using (EntityConnection conn = new EntityConnection(strConn))
                {
                        conn.Open();

                        try
                        {
                                // EntityCommand - 对 EDM 执行的命令
                                //         CommandType - 命令类型 [System.Data.CommandType枚举]
                                //                 CommandType.Text - esql语句。默认值
                                //                 CommandType.StoredProcedure - 存储过程名
                                //                 CommandType.TableDirect - 表名
                                //         CommandText - 命令文本。esql语句或存储过程名或表名
                                //         CommandTimeout - 超时时间。单位：秒
                                using (EntityCommand cmd = conn.CreateCommand())
                                {
                                        cmd.CommandType = CommandType.Text;
                                        cmd.CommandText = "select value c from NorthwindEntities.Categories as c";

                                        // EntityDataReader - 以只读、只进的数据流的方式获取数据（内存中始终只有一行）。相当于SqlDataReader
                                        //         Read() - 读下一条记录
                                        //         HasRows() - 是否还有可读数据
                                        //         Close() - 关闭 EntityDataReader
                                        // EntityCommand.ExecuteReader() - 执行命令，返回 EntityDataReader 对象
                                        using (EntityDataReader edr = cmd.ExecuteReader(CommandBehavior.SequentialAccess))
                                        {
                                                 while (edr.Read())
                                                {
                                                        result.InnerHtml += edr[ "CategoryName"].ToString() + "<br />";
                                                }
                                        }
                                }
                        }
                        catch (Exception ex)
                        {
                                result.InnerHtml += ex.ToString();
                        }
                        finally
                        {
                                conn.Close();
                        }
                }

                /**//*
                 SELECT    
                [Extent1].[CategoryID] AS [CategoryID],    
                [Extent1].[CategoryName] AS [CategoryName],    
                [Extent1].[Description] AS [Description],    
                [Extent1].[Picture] AS [Picture]
                FROM [dbo].[Categories] AS [Extent1]
                */
        }

        void Demo2()
        {
                // EntityConnection 构造函数的参数为 name = web.config中的connectionStrings中配置的连接字符串的name
                using (EntityConnection conn = new EntityConnection( "name = NorthwindEntities"))
                {
                        conn.Open();

                        try
                        {
                                using (EntityCommand cmd = conn.CreateCommand())
                                {
                                        cmd.CommandType = CommandType.Text;
                                        cmd.CommandText = "select value s from NorthwindEntities.categories as s where s.categoryId = @categoryId";

                                        // EntityParameter - 配置 EntityCommand 的参数
                                        //         ParameterName - 参数名
                                        //         Value- 参数值
                                        //         Size - 参数大小
                                        //         DbTyp - 参数类型 [System.Data.DbType 枚举]
                                        //         IsNullable - 是否接受 null 值
                                        EntityParameter param = new EntityParameter();
                                        param.ParameterName = "categoryId";
                                        param.Value = 1;

                                        // EntityCommand.Parameters.Add() - 为 EntityCommand 增加参数
                                        cmd.Parameters.Add(param);

                                        using (EntityDataReader edr = cmd.ExecuteReader(CommandBehavior.SequentialAccess))
                                        {
                                                 while (edr.Read())
                                                {
                                                        result.InnerHtml += edr.GetString(1) + "<br />";
                                                }
                                        }
                                }
                        }
                        catch (Exception ex)
                        {
                                result.InnerHtml += ex.ToString();
                        }
                        finally
                        {
                                conn.Close();
                        }
                }

                /**//*
                exec sp_executesql N 'SELECT    
                [Extent1].[CategoryID] AS [CategoryID],    
                [Extent1].[CategoryName] AS [CategoryName],    
                [Extent1].[Description] AS [Description],    
                [Extent1].[Picture] AS [Picture]
                FROM [dbo].[Categories] AS [Extent1]
                WHERE [Extent1].[CategoryID] = @categoryId ',N'@categoryId int',@categoryId=1
                */
        }

        void Demo3()
        {
                // EntityConnectionStringBuilder - 构造连接字符串
                EntityConnectionStringBuilder entityBuilder = new EntityConnectionStringBuilder();
                entityBuilder.Provider = "System.Data.SqlClient";
                entityBuilder.ProviderConnectionString = @"Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\Northwind.mdf;Integrated Security=True;User Instance=True;MultipleActiveResultSets=True";
                entityBuilder.Metadata = @"res://*/Northwind.csdl|res://*/Northwind.ssdl|res://*/Northwind.msl";

                using (EntityConnection conn = new EntityConnection(entityBuilder.ConnectionString))
                {
                        conn.Open();

                        try
                        {
                                using (EntityCommand cmd = conn.CreateCommand())
                                {
                                        // 调用存储过程（需要先做好映射，然后指定概念模型中的函数名称）
                                        cmd.CommandType = CommandType.StoredProcedure;
                                        cmd.CommandText = "NorthwindEntities.GetCategory";

                                        EntityParameter param = new EntityParameter();
                                        param.ParameterName = "CategoryID";
                                        param.Value = 1;
                                        cmd.Parameters.Add(param);

                                        using (EntityDataReader edr = cmd.ExecuteReader(CommandBehavior.SequentialAccess))
                                        {
                                                 while (edr.Read())
                                                {
                                                        result.InnerHtml += edr[ "CategoryName"].ToString() + "<br />";
                                                }
                                        }
                                }
                        }
                        catch (Exception ex)
                        {
                                result.InnerHtml += ex.ToString();
                        }
                        finally
                        {
                                conn.Close();
                        }
                }

                /**//*
                exec [dbo].[spSelectCategory] @CategoryID=1    
                */
        }
}

 

 

2、关于ObjectQuery
ObjectQuery.aspx.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

using System.Data.Objects;
using System.Data.Objects.DataClasses;
using System.Data.EntityClient;
using System.Data;
using System.Data.Common;

using VS2008SP1.Business;

public partial class EntityFramework_ObjectQuery : System.Web.UI.Page
{
void Page_Load() void Page_Load(object sender, EventArgs e)
        {
                 if (!Page.IsPostBack)
                {
                        Demo();

                        result.InnerHtml += "<br />";

                        Demo2();

                        result.InnerHtml += "<br />";

                        Demo3();

                        result.InnerHtml += "<br />";

                        Demo4();
                }
        }

void Demo() void Demo()
        {
                using (var ctx = new NorthwindEntities())
                {
                         string esql = "select value c from NorthwindEntities.Categories as c";

                        // ObjectQuery<T> - 通过 Entity SQL 或 查询语法 或 Linq 方法对概念模型做查询
                        // ObjectContext.CreateQuery<T>(Entity SQL) - 根据 esql 创建一个 ObjectQuery<T> 。（延迟）
                        ObjectQuery<Categories> query = ctx.CreateQuery<Categories>(esql);

                        foreach (var c in query)
                        {
                                result.InnerHtml += c.CategoryName + "<br />";
                        }
                }

                /**//*
                 SELECT    
                [Extent1].[CategoryID] AS [CategoryID],    
                [Extent1].[CategoryName] AS [CategoryName],    
                [Extent1].[Description] AS [Description],    
                [Extent1].[Picture] AS [Picture]
                FROM [dbo].[Categories] AS [Extent1]
                */
        }

void Demo2() void Demo2()
        {
                using (var ctx = new NorthwindEntities())
                {
                         string esql = "select c.CategoryName from NorthwindEntities.Categories as c";

                        // ObjectQuery<T>()构造函数 - 根据 esql 创建一个 ObjectQuery ，返回 DbDataRecord 。（延迟）
                        // System.Data.Objects.MergeOption枚举 - 如何将此次查询结果与之前同一 ObjectContext 的存在与内存的查询结果做合并
                        //         MergeOption.AppendOnly - 追加。默认值
                        //         MergeOption.OverwriteChanges - 以新结果为准
                        //         MergeOption.PreserveChanges - 以原结果为准
                        //         MergeOption.NoTracking - 取消变更跟踪，不会使用 ObjectStateManager，减少执行查询的时间，所有返回的实体将是分离的状态（detached state）
                        ObjectQuery<DbDataRecord> query = new ObjectQuery<DbDataRecord>(esql, ctx, MergeOption.NoTracking);

                        // 可以在 ObjectQuery<T> 上使用 Linq 方法或查询语法
                        foreach (DbDataRecord item in query.Take(3))
                        {
                                result.InnerHtml += item[ "CategoryName"].ToString() + "<br />";
                        }
                }

                /**//*
                 SELECT    
                [Limit1].[C1] AS [C1],    
                [Limit1].[CategoryName] AS [CategoryName]
                FROM ( SELECT TOP (3)    
                        [Extent1].[CategoryName] AS [CategoryName],    
                        1 AS [C1]
                        FROM [dbo].[Categories] AS [Extent1]
                )     AS [Limit1]
                */
        }

void Demo3() void Demo3()
        {
                using (var ctx = new NorthwindEntities())
                {
                         string esql = "select value count(c.CategoryID) from NorthwindEntities.Categories as c";

                        // ObjectQuery<简单类型> 的示例（延迟）
                        ObjectQuery<int> query = ctx.CreateQuery<int>(esql);

                        result.InnerHtml += query.First().ToString() + "<br />";
                }

                /**//*
                 SELECT    
                [Limit1].[A1] AS [C1]
                FROM ( SELECT TOP (1)    
                        COUNT([Extent1].[CategoryID]) AS [A1]
                        FROM [dbo].[Categories] AS [Extent1]
                )     AS [Limit1]    
                */
        }

void Demo4() void Demo4()
        {
                using (var ctx = new NorthwindEntities())
                {
                         string esql = "select value c from NorthwindEntities.Categories as c";
                        
                        // 延迟
                        ObjectQuery<Categories> query = ctx.CreateQuery<Categories>(esql);

                        // ObjectQuery<T>. Execute() - 立即执行查询。返回 ObjectResult<T>
                        ObjectResult<Categories> queryResult = query. Execute(MergeOption.NoTracking);

                        foreach (var c in queryResult)
                        {
                                result.InnerHtml += c.CategoryName + "<br />";
                        }
                }

                /**//*
                 SELECT    
                [Extent1].[CategoryID] AS [CategoryID],    
                [Extent1].[CategoryName] AS [CategoryName],    
                [Extent1].[Description] AS [Description],    
                [Extent1].[Picture] AS [Picture]
                FROM [dbo].[Categories] AS [Extent1]    
                */
        }
}

 

 

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