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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

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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
    {
        
    protected 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
    {
        
    protected void Page_Load(object sender, EventArgs e)
        
    {
            
    if (!Page.IsPostBack)
            
    {
                Demo();

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

                Demo2();

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

                Demo3();

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

                Demo4();
            }

        }


        
    private 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]
            
    */

        }


        
    private 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]
            
    */

        }


        
    private 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] 
            
    */

        }


        
    private 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] 
            
    */

        }

    }


    OK
    [源码下载]
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  • 原文地址:https://www.cnblogs.com/webabcd/p/1384236.html
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