再接再厉VS 2008 sp1 + .NET 3.5 sp1(4) - Entity Framework(实体框架)之EntityClient, ObjectQuery-阿里云开发者社区

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 += " ";

 Demo2();

 result.InnerHtml += " ";

 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() + " ";
 }
 }
 }
 }
 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) + " ";
 }
 }
 }
 }
 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() + " ";
 }
 }
 }
 }
 catch (Exception ex)
 {
 result.InnerHtml += ex.ToString();
 }
 finally
 {
 conn.Close();
 }
 }

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

2、关于ObjectQuery
ObjectQuery.aspx.cs