Entity Framework快速入门--实例篇 DatabaseFirst

在上一篇中我们简单了解的EF的定义和大体的情况，我们通过一步一步的做一个简单的实际例子来让大家对EF使用有个简单印象。好，废话少说，直入主题。

第一步：创建控制台项目

这个就不多说了，如果新建项目你还不知道，那先去学学基础吧。

第二步：创建实体模型

在项目上右击添加新建项目→Ado.Net实体数据模型

如下图所示：

第三步：与现有的数据库进行连接生成EF实体

在做这步之前，首先确定你是否已经有现有数据库，当然在这提供我自己的数据库脚本。

View Code

-- --------------------------------------------------
-- Entity Designer DDL Script for SQL Server 2005, 2008, and Azure
-- --------------------------------------------------
-- Date Created: 02/20/2011 09:47:54
-- Generated from EDMX file: E:\Job\projects\WebTest\EF\Model1.edmx
-- --------------------------------------------------

SET QUOTED_IDENTIFIER OFF;
GO
USE [SchoolDB];
GO
IF SCHEMA_ID(N'dbo') IS NULL EXECUTE(N'CREATE SCHEMA [dbo]');
GO

-- --------------------------------------------------
-- Dropping existing FOREIGN KEY constraints
-- --------------------------------------------------

IF OBJECT_ID(N'[dbo].[FK_ClassStudent]', 'F') IS NOT NULL
ALTER TABLE [dbo].[T_Student] DROP CONSTRAINT [FK_ClassStudent];
GO
IF OBJECT_ID(N'[dbo].[FK_ClassTeacher]', 'F') IS NOT NULL
ALTER TABLE [dbo].[T_Teacher] DROP CONSTRAINT [FK_ClassTeacher];
GO

-- --------------------------------------------------
-- Dropping existing tables
-- --------------------------------------------------

IF OBJECT_ID(N'[dbo].[T_Class]', 'U') IS NOT NULL
DROP TABLE [dbo].[T_Class];
GO
IF OBJECT_ID(N'[dbo].[T_Student]', 'U') IS NOT NULL
DROP TABLE [dbo].[T_Student];
GO
IF OBJECT_ID(N'[dbo].[T_Teacher]', 'U') IS NOT NULL
DROP TABLE [dbo].[T_Teacher];
GO

-- --------------------------------------------------
-- Creating all tables
-- --------------------------------------------------

-- Creating table 'T_Class'
CREATE TABLE [dbo].[T_Class] (
[ID] int IDENTITY(1,1) NOT NULL,
[Name] nvarchar(max) NOT NULL
);
GO

-- Creating table 'T_Student'
CREATE TABLE [dbo].[T_Student] (
[ID] uniqueidentifier NOT NULL,
[Name] nvarchar(max) NOT NULL,
[ClassID] int NOT NULL,
[Phone] nvarchar(max) NOT NULL,
[Email] nvarchar(max) NOT NULL
);
GO

-- Creating table 'T_Teacher'
CREATE TABLE [dbo].[T_Teacher] (
[ID] int IDENTITY(1,1) NOT NULL,
[Name] nvarchar(max) NOT NULL,
[Address] nvarchar(max) NOT NULL,
[Phone] nvarchar(max) NOT NULL,
[Email] nvarchar(max) NOT NULL,
[ClassID] int NOT NULL
);
GO

-- --------------------------------------------------
-- Creating all PRIMARY KEY constraints
-- --------------------------------------------------

-- Creating primary key on [ID] in table 'T_Class'
ALTER TABLE [dbo].[T_Class]
ADD CONSTRAINT [PK_T_Class]
PRIMARY KEY CLUSTERED ([ID] ASC);
GO

-- Creating primary key on [ID] in table 'T_Student'
ALTER TABLE [dbo].[T_Student]
ADD CONSTRAINT [PK_T_Student]
PRIMARY KEY CLUSTERED ([ID] ASC);
GO

-- Creating primary key on [ID] in table 'T_Teacher'
ALTER TABLE [dbo].[T_Teacher]
ADD CONSTRAINT [PK_T_Teacher]
PRIMARY KEY CLUSTERED ([ID] ASC);
GO

-- --------------------------------------------------
-- Creating all FOREIGN KEY constraints
-- --------------------------------------------------

-- Creating foreign key on [ClassID] in table 'T_Student'
ALTER TABLE [dbo].[T_Student]
ADD CONSTRAINT [FK_ClassStudent]
FOREIGN KEY ([ClassID])
REFERENCES [dbo].[T_Class]
([ID])
ON DELETE NO ACTION ON UPDATE NO ACTION;

-- Creating non-clustered index for FOREIGN KEY 'FK_ClassStudent'
CREATE INDEX [IX_FK_ClassStudent]
ON [dbo].[T_Student]
([ClassID]);
GO

-- Creating foreign key on [ClassID] in table 'T_Teacher'
ALTER TABLE [dbo].[T_Teacher]
ADD CONSTRAINT [FK_ClassTeacher]
FOREIGN KEY ([ClassID])
REFERENCES [dbo].[T_Class]
([ID])
ON DELETE NO ACTION ON UPDATE NO ACTION;

-- Creating non-clustered index for FOREIGN KEY 'FK_ClassTeacher'
CREATE INDEX [IX_FK_ClassTeacher]
ON [dbo].[T_Teacher]
([ClassID]);
GO

-- --------------------------------------------------
-- Script has ended
-- --------------------------------------------------

然后按照如下所示，选择从数据库生成实体数据模型【当然如果你想使用CodeFirst方式也是可以的，这是后话了】：

新建连接到现有的数据库，如下图所示：

点击下一步，选择我们要生成实体对应的表、试图、存储过程等，如下图所示：

最后点击完成，则系统帮我们生成了数据库实体类以及EDMX的定义文件。

如图所示：

到现在我们前期的准备工作就结束了，我们接下来看看我们怎么使用EF帮我们生成的数据库网关

第四步：写增删改查来讲解EF的基本使用

添加如下代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace EF
{
class Program
{
static void Main(string[] args)
{
//创建数据库访问网关
using (SchoolDBEntities schoolEntities = new SchoolDBEntities())
{
//查询到老师对应的班级的外键，注意是使用的linq to ef ,它是生成的命令树，然后是生成的sql

var cls = (from c in schoolEntities.T_Class
where c.ID == 2
select c).SingleOrDefault<T_Class>();
//创建teacher一个实体
T_Teacher teacher = new T_Teacher();
teacher.Address = "北京海淀上地";
teacher.Email = "malun666@126.com";
teacher.T_Class = cls;

teacher.Name = "Flydragon";
teacher.Phone = "110";
//将创建的实体，放入网关的数据实体的集合
schoolEntities.T_Teacher.AddObject(teacher);
//写回数据库
schoolEntities.SaveChanges();
}
Console.WriteLine("OK");
}
}
}

最终数据库中添加了一条数据，如下图所示：