精进不休 .NET 4.0 (7) - ADO.NET Entity Framework 4.0 新特性

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精进不休 .NET 4.0 (7) - ADO.NET Entity Framework 4.0 新特性

作者： webabcd


介绍
ADO.NET Entity Framework 4.0 的新增功能

• 对外键的支持，即把外键当做实体的一个属性来处理 
• 对复杂类型的支持，即实体属性可以是一个复杂类型 
• 将多个表映射到一个概念实体，将一个表拆为多个概念实体 
• 增强了 LINQ to Entities
• 新增了对 POCO（Plain Old CLR Object）的支持，即 Model 代码中不会有任何关于持久化的代码 
• 其他新特性

示例
1、外键 的 Demo
EntityFramework/ForeignKeys/Demo.aspx.cs

/*
* ADO.NET Entity Framework 4.0 - 新增了对外键的支持，即把外键当做实体的一个属性来处理
*/

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

namespace DataAccess.EntityFramework.ForeignKeys
{
         public partial class Demo : System.Web.UI.Page
        {
Random _random = new Random() Random _random = new Random();
void Page_Load() void Page_Load(object sender, EventArgs e)
                {
                        // 在一个已存在的产品类别下新建一个产品（通过外键值）
                        using (var ctx = new ForeignKeysEntities())
                        {
                                Product p = new Product
                                {
                                        Name = "webabcd test" + _random. Next().ToString(),
                                        ProductNumber = _random. Next().ToString(),
                                        StandardCost = 1,
                                        ListPrice = 1,
                                        SellStartDate = DateTime.Now,
                                        rowguid = Guid.NewGuid(),
                                        ModifiedDate = DateTime.Now,
                                        ProductCategoryID = 18
                                };

                                // 这里需要手工 Add 这个新的 Product，然后再调用 SaveChanges()
                                ctx.Products.AddObject(p);
                                Response.Write(ctx.SaveChanges());
                        }

                        Response.Write( "<br /><br />");

                        // 在一个已存在的产品类别下新建一个产品（通过外键对象）
                        using (var ctx = new ForeignKeysEntities())
                        {
                                Product p = new Product
                                {
                                        Name = "webabcd test" + _random. Next().ToString(),
                                        ProductNumber = _random. Next().ToString(),
                                        StandardCost = 1,
                                        ListPrice = 1,
                                        SellStartDate = DateTime.Now,
                                        rowguid = Guid.NewGuid(),
                                        ModifiedDate = DateTime.Now,
                                        ProductCategory = ctx.ProductCategories.Single(c => c.ProductCategoryID == 18)
                                };
                                
                                // 这里直接调用 SaveChanges() 即可，而不用再手工地 Add 这个新的 Product
                                // 因为与这个新的 Product 关联的那个已存在的 ProductCategory 会自动地 Add 这个新的 Product
                                Response.Write(ctx.SaveChanges());
                        }
                }
        }
}

 

 

2、复杂类型的 Demo
EntityFramework/ComplexType/Demo.aspx.cs

/*
* ADO.NET Entity Framework 4.0 - 新增了对复杂类型的支持，即实体属性可以是一个复杂类型
* 1、在 EDM 设计器中的实体上，点击右键，在“Add”选项中可以新建一个复杂类型
* 2、在 EDM 设计器中的实体上，选中多个属性后，点击右键，选择“Refactor into New Complex Type”可以合并多个属性为一个复杂类型
* 3、在 EDM 设计器中的“Mapping Details”窗口或“Model Broswer”窗口里，可以对复杂类型做编辑
*    
* ADO.NET Entity Framework 4.0 - 对存储过程的支持有了明显的增强
* 表现为：可以将存储过程的返回值映射到一个自定义的复杂类型上，当然，这个复杂类型也可以根据储过程的返回值自动生成
*/

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

namespace DataAccess.EntityFramework.ComplexType
{
         public partial class Demo : System.Web.UI.Page
        {
void Page_Load() void Page_Load(object sender, EventArgs e)
                {
                        using (var ctx = new ComplexTypeEntities())
                        {
                                // 这里的 Name 类型是自定义的一个复杂类型（其有三个属性，分别为FirstName, MiddleName, LastName），详见 EDM
                                Name name = ctx.Customers.First().Name;

                                Response.Write( string.Format( "FirstName: {0}<br />MiddleName: {1}<br />LastName: {2}", name.FirstName, name.MiddleName, name.LastName));
                        }

                        Response.Write( "<br /><br />");

                        using (var ctx = new ComplexTypeEntities())
                        {
                                // 这里的 MyCustomer 类型，是存储过程 uspSelectCustomer（其概念模型为：GetCustomer()） 的返回值的映射类型
                                MyCustomer customer = ctx.GetCustomer().First();
                                
                                Response.Write( string.Format( "CustomerID: {0}<br />FirstName: {1}<br />MiddleName: {2}<br />LastName: {3}", customer.CustomerID, customer.FirstName, customer.MiddleName, customer.LastName));
                        }
                }
        }
}

 

 

3、将一个表拆为多个概念实体的 Demo
EntityFramework/TableSplitting/Demo.aspx.cs

/*
1、将多个表映射到一个概念实体，原来就可以。在 EDM 设计器中将两个一对一的表映射到一个实体即可
2、将一个表拆为多个概念实体，原来也行，但是要在 xml 中手工配置。现在 VS2010 中只需在 EDM 设计器中做如下设置：
        a、新建两个实体，做好相关字段相对于原表的映射
        b、在这两个实体间新建一个一对一的关联
        c、双击这个关联线，编辑约束，指明主表和依赖表，并设置相关的主键
*/

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

namespace DataAccess.EntityFramework.TableSplitting
{
         public partial class Demo : System.Web.UI.Page
        {
void Page_Load() void Page_Load(object sender, EventArgs e)
                {
                        // 将一个 ErrorLog 表映射到两个实体上 ErrorLog 和 ErrorLogExt，详见 EDM
                        using (var ctx = new TableSplittingEntities())
                        {
                                ErrorLog log = ctx.ErrorLogs.First();
                                Response.Write(log.ErrorLogID);

                                Response.Write( "<br />");

                                log.ErrorLogExtReference.Load();
                                Response.Write(log.ErrorLogExt.ErrorMessage);
                        }
                }
        }
}

 

 

4、LINQ to Entities 新功能的 Demo
EntityFramework/LINQ2Entities/Demo.aspx.cs

/*
* ADO.NET Entity Framework 4.0 - 增强了 LINQ to Entities
*/

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.Common;

namespace DataAccess.EntityFramework.LINQ2Entities
{
         public partial class Demo : System.Web.UI.Page
        {
void Page_Load() void Page_Load(object sender, EventArgs e)
                {
                        Demo1();
                        Demo2();

                        // 支持 Single() 扩展方法了，之前的版本不支持
                }

void Demo1() void Demo1()
                {
                        // ADO.NET Entity Framework 4.0 - 新增了 System.Data.Objects.EntityFunctions 和 System.Data.Objects.SqlClient.SqlFunctions
                        // 其作用相当于 Linq to Sql 中的 System.Data.Linq.SqlClient.SqlMethods
                        using (var ctx = new LINQ2EntitiesEntities())
                        {
                                var products =
                                            from p in ctx.Products
                                            where System.Data.Objects.SqlClient.SqlFunctions.DateDiff( "year", p.SellStartDate, DateTime.Now) <= 10
                                             select p;
                                
                                Response.Write((products as System.Data.Objects.ObjectQuery).ToTraceString());
                                Response.Write( "<br />");
                                Response.Write( "十年内销售的产品数量为：" + products.Count());
                        }

                        Response.Write( "<br /><br />");

                        // 上面的示例如果写成 esql 就是如下的写法。当然这个原来就支持。
                        using (var ctx = new LINQ2EntitiesEntities())
                        {
                                 string esql = "select value p from LINQ2EntitiesEntities.Products as p where SqlServer.DATEDIFF('year', p.SellStartDate, SqlServer.GETDATE()) <= 10";
                                // string esql = "using SqlServer; select value p from LINQ2EntitiesEntities.Products as p where DATEDIFF('year', p.SellStartDate, GETDATE()) <= 10";

                                ObjectQuery<Product> products = ctx.CreateQuery<Product>(esql);

                                Response.Write(products.ToTraceString());
                                Response.Write( "<br />");
                                Response.Write( "十年内销售的产品数量为：" + products.Count());
                        }

                        Response.Write( "<br /><br />");
                }

void Demo2() void Demo2()
                {
                        // 使用 esql 的方式调用 sql 中的用户自定义函数
                        using (var ctx = new LINQ2EntitiesEntities())
                        {
                                 string esql = "select value top(1) LINQ2EntitiesModel.Store.ufnGetFullName(c.firstName, c.middleName, c.lastName) from LINQ2EntitiesEntities.Customers as c";

                                ObjectQuery< string> customers = ctx.CreateQuery< string>(esql);

                                Response.Write((customers as System.Data.Objects.ObjectQuery).ToTraceString());
                                Response.Write( "<br />");

                                foreach (var customerName in customers.ToList())
                                {
                                        Response.Write(customerName);
                                        Response.Write( "<br />");
                                }
                        }

                        Response.Write( "<br /><br />");

                        // clr 的方式调用 sql 的用户自定义函数。具体实现见 MyClass 类
                        using (var ctx = new LINQ2EntitiesEntities())
                        {
                                var customers =
                                        from c in ctx.Customers
                                         select MyClass.GetFullName(c.FirstName, c.MiddleName, c.LastName);
                                customers = customers.Take(1);

                                Response.Write((customers as System.Data.Objects.ObjectQuery).ToTraceString());
                                Response.Write( "<br />");

                                foreach (var customerName in customers.ToList())
                                {
                                        Response.Write(customerName);
                                        Response.Write( "<br />");
                                }
                        }
                }
                
                 public static class MyClass
                {
                        
                        // System.Data.Objects.DataClasses.EdmFunction( string namespaceName, string functionName) - 将 sql 中的指定的用户自定义函数映射到 clr 的方法上
                        //         string namespaceName - SSDL（存储模型）的命名空间，可以在 edmx 文件中找到这个值
                        //         string functionName - sql 中的用户自定义函数名
                        [System.Data.Objects.DataClasses.EdmFunction( "LINQ2EntitiesModel.Store", "ufnGetFullName")]
                        /// <summary>
                        /// 此方法的参数要与其所映射的 sql 用户自定义函数的参数相匹配
                        /// 此方法只可用于 linq 表达式，方法内不用做任何实现
                        /// </summary>
static string GetFullName() static string GetFullName( string firstName, string middleName, string lastName)
                        {
                                throw new NotSupportedException( "You can only call this method as part of a LINQ expression");
                        }
                }
        }
}

 

 

5、POCO 的 Demo
Demo.aspx

<%@ Page Language= "C#" AutoEventWireup= "true" CodeBehind= "Demo.aspx.cs" Inherits= "POCODemo.Demo" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns= "http://www.w3.org/1999/xhtml">
<head runat= "server">
        <title></title>
</head>
<body>
        <form id= "form1" runat= "server">
        <div>
                ADO.NET Entity Framework 4.0 - 新增了对 POCO（Plain Old CLR Object）的支持，即 Model 代码中不会有任何关于持久化的代码
                <ul>
                        <li>1、线上有 POCO 的 T4（Text Template Transformation Toolkit）模板</li>
                        <li>2、在 EDM 设计器上单击右键，选择“Add Code Generation Item”，在线上模板中选择“ADO.NET C# POCO Entity Generator”模板生成即可</li>
                        <li>3、在 EF 中，POCO 与非 POCO 不能在一个项目中共存，因为非 POCO 的 EF 在 assembly 级别上会有如下声明<br />
                                using System.Data.Objects.DataClasses;<br />
                                [assembly: EdmSchemaAttribute()]<br />
                                而 POCO 不需要这个声明，所以一个程序集内不能既有 POCO 又有非 POCO </li>
                        <li>4、具体的 POCO 代码，详见本例中的由 POCO 模板生成的代码 </li>
                </ul>
        </div>
        </form>
</body>
</html>

 

 

6、其他新特性
EntityFramework/Others.aspx

<%@ Page Title= "其它，一笔带过" Language= "C#" MasterPageFile= "~/Site.Master" AutoEventWireup= "true"
        CodeBehind= "Others.aspx.cs" Inherits= "DataAccess.EntityFramework.Others" %>

<asp:Content ID= "Content1" ContentPlaceHolderID= "head" runat= "server">
</asp:Content>
<asp:Content ID= "Content2" ContentPlaceHolderID= "ContentPlaceHolder1" runat= "server">
        <p>
                1、T4 模板引擎（微软的一个代码生成引擎） - Text Template Transformation Toolkit
        </p>
        <p>
                2、增强了 EDM 设计器
        </p>
        <p>
                3、对 Model-First 的支持，即根据概念模型生成存储模型和映射模型
                <ul>
                        <li>在概念模型（EDM 设计器）上单击右键，选择“ Generate Database from Model”，即可生成数据库脚本</li>
                        <li>
                                在 EDM 设计器中，与 Model-First 相关的字段属性说明
                                <ul>
                                        <li>StoreGeneratedPattern - 该字段所对应的数据库中的列属性（有三种：无，自增，通过计算而来）</li>
                                        <li>FixedLength - FixedLength= true 对应 nchar, FixedLength= false 对应 nvarchar</li>
                                        <li>Unicode - 是否是 Unicode 编码。比如字符串如果是非 Unicode 则对应 varchar，如果是 Unicode 则对应 nvarchar</li>
                                        <li>Max Length - 最大字符数。对应 varchar(n) 或 nvarchar(n) 中的 n</li>
                                </ul>
                        </li>
                </ul>
        </p>
        <p>
                4、Code Only - 在 POCO 的基础上，连 EDM 也不需要了（即不用再做概念模型，映射模型，存储模型的配置）， 纯写代码即可，可惜在 EF 4.0 的正式版里这个功能被去掉了
        </p>
        <p>
                5、 改进了 SQL 语句的生成
        </p>
        <p>
                6、Lazy Loading - 支持延迟加载，相关设置 context.ContextOptions.DeferredLoadingEnabled = true; 其默认值就是 true
        </p>
        <p>
                7、 Explicit Loading - 显示加载，看下面的例子
                <ul>
                        <li>加载导航属性的方法如下（当然 Include 也可以达到同样的效果）context.LoadProperty(category, "Products");</li>
                        <li>上面那个方法（包括 Include）不太好，因为如果实体集名称写错的话 runtime 的时候是才能发现，所以为了避免写错可以使用如下方法 context.LoadProperty(category, c => c.Products);</li>
                </ul>
        </p>
        <p>
                8、几种自带的 T4 模板的说明
                <ul>
                        <li>ADO.NET EntityObject Generator - 把 edmx 文件中的内联代码摘出来</li>
                        <li>ADO.NET POCO Entity Generator - 生成 POCO（Plain Old CLR Object） 实体，其包括每个表所映射的实体及一个Context，POCO 中不会包含持久化相关的代码（这个模板非内置，可以在线上模板中找到）</li>
                        <li>ADO.NET Self-Tracking Entity Generator - POCO 的加强版，在 POCO 的基础上增加了实体状态自跟踪的功能</li>
                </ul>
        </p>
        <p>
                9、新建 EDM 的时候，在向导中有一个选项“pluralize or singularize generated object names”，其意思为：生成对应的 Model 时，实体名称自动用单数形式，实体集名称自动用复数形式
        </p>
</asp:Content>

 

 

OK
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