17.C#:Entity Framework快速入门--实例篇
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之前的那篇MSDN上翻译过来的EF写得并不好,没有操作性,这里结合网上一片有实例的博客,结合自己的操作过程,作以下说明:
1.使用VS2010和C#语言,所以要有Oracle数据库服务器,并且要安装VS和Oracle之间的连接组件,我这里安装为:Oracle Data Access Components for Oracle Client
2.连接数据库后,在PL/SQL Devoloper里面写好SQL建表语句,创建序列和触发器语句(用于主键,否则不能有主键,不然异常提示不符合唯一性约束),运行,提交
3.按照下面博客创建Entity Framework实例,将表格等映射为VS中的类等实体
4.在VS主函数里面写好下面博客里面的代码,运行即可到PL/SQL Devoloper查看修改结果
5.PL/SQL Devoloper里面的代码:
建表:
create table T_Class( ID number(8) primary key not null, Name varchar(20));create table T_Student( ID number(8) primary key not null, Name varchar(20), ClassID number(8), Phone varchar(20), Email varchar(30), constraint T_Student2T_Class foreign key(ClassID) references T_Class(ID) on delete cascade);create table T_Teacher( ID number(8) primary key not null, Name varchar(20), Address varchar(30), Phone varchar(20), Email varchar(30), ClassID number(8), constraint T_Teacher2T_Class foreign key(ClassID) references T_Class(ID) on delete cascade); /*drop table T_Student;drop table T_Class;drop table T_Teacher;*//*insert into T_Class values(2,'Class1'); */select * from T_Teacher;select * from T_Class;delete from T_Teacher;--序列create sequence SEQ_T_TEACHERminvalue 1maxvalue 9999999999999999999999999999start with 2increment by 1cache 20;--触发器create or replace trigger tib_T_Teacher before inserton T_Teacher for each rowdeclare integrity_error exception; errno integer; errmsg char(200); dummy integer; found boolean;begin if :new.ID is null or :new.ID = 0 then select SEQ_T_Teacher.NEXTVAL INTO :new.ID from dual; end if;exception when integrity_error then raise_application_error(errno, errmsg);end;
6.VS2010代码(跟下面一致,多了几句解释)
using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace myEF{ class Program { static void Main(string[] args) { //schoolEntities.T_CLASS表示T_Class表,而c表示一条记录结构 using (var schoolEntities = new SchoolDBEntities()) { var cls = (from c in schoolEntities.T_CLASS where c.ID == 2 select c).SingleOrDefault<T_CLASS>(); //如果要表示所有记录,必须使用list集合 //List<T_TEACHER> tList = new List<T_TEACHER>(); //T_Teacher表示表结构,teacher.T_CLASS表示teacher的外键所在表的表结构 T_TEACHER teacher = new T_TEACHER(); //teacher.ID = new Random().Next(); teacher.ADDRESS = "北京海淀上地"; teacher.EMAIL = "malun666@126.com"; teacher.T_CLASS = cls; teacher.NAME = "Flydragon"; teacher.PHONE = "110"; schoolEntities.T_TEACHER.AddObject(teacher); Console.WriteLine("in"); try { schoolEntities.SaveChanges(); } catch (Exception ex) { } } Console.WriteLine("OK"); Console.ReadKey(); } }}
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。
-- --------------------------------------------------
-- 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:
然后我正好打开了Sql Server Profiler工具我们看一下,EF生成的SQL语句是什么,如下图所示:
最后一个就是执行insert插入数据库表的sql,如下图所示:
好这样我们一个入门的实例程序,就结束了,我们看到最后EF还是生成的SQL执行的。所以EF本身性能的损失也就是根据对实体集合的修改,然后根据edmx的定义最终成sql这段,也就是浪费了点cpu而已,而且ef还会自动帮我们对sql进行优化,所以还是蛮不错的!
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