利用mybatis实现增删改查 的小项目，单表，双表一对多，

简介：
MyBatis 本是apache的一个开源项目iBatis, 2010年这个项目由apache software foundation 迁移到了google code，并且改名为MyBatis 。2013年11月迁移到Github。

iBATIS一词来源于”internet”和”abatis”的组合，是一个基于Java的持久层框架。iBATIS提供的持久层框架包括SQL Maps和Data Access Objects(DAO)
MyBatis 是支持普通 SQL查询，存储过程和高级映射的优秀持久层框架。MyBatis 消除了几乎所有的JDBC代码和参数的手工设置以及结果集的检索。MyBatis 使用简单的 XML或注解用于配置和原始映射，将接口和 Java 的POJOs(Plain Old Java Objects，普通的 Java对象)映射成数据库中的记录。

每个MyBatis应用程序主要都是使用SqlSessionFactory实例的，一个SqlSessionFactory实例可以通过SqlSessionFactoryBuilder获得。SqlSessionFactoryBuilder可以从一个xml配置文件或者一个预定义的配置类的实例获得。
下面开始我们的小项目：
1.我们已经在自己的数据库中建立好了将要展示的三个表，并添加好了某些数据
user表：

CREATE TABLE `user` (
    `id` INT(11) NOT NULL AUTO_INCREMENT,
    `username` VARCHAR(50) NOT NULL COLLATE 'utf8_bin',
    `psw` VARCHAR(50) NOT NULL COLLATE 'utf8_bin',
    PRIMARY KEY (`id`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB
AUTO_INCREMENT=12
;

Company表：

CREATE TABLE `company` (
    `cid` INT(11) NOT NULL,
    `name` VARCHAR(10) NOT NULL COLLATE 'utf8_bin',
    `address` VARCHAR(10) NOT NULL COLLATE 'utf8_bin',
    `pro` VARCHAR(10) NOT NULL COLLATE 'utf8_bin',
    `city` VARCHAR(10) NOT NULL COLLATE 'utf8_bin',
    `price` FLOAT NULL DEFAULT NULL,
    PRIMARY KEY (`cid`)
)
COLLATE='latin1_swedish_ci'
ENGINE=InnoDB
;

Emp表：

CREATE TABLE `emp` (
    `eid` INT(11) NOT NULL,
    `name` VARCHAR(10) NOT NULL COLLATE 'utf8_bin',
    `sex` VARCHAR(2) NULL DEFAULT NULL,
    `email` VARCHAR(50) NULL DEFAULT NULL,
    `salary` FLOAT NULL DEFAULT NULL,
    `cid` INT(11) NULL DEFAULT NULL,
    PRIMARY KEY (`eid`),
    INDEX `c_e_cid` (`cid`),
    CONSTRAINT `c_e_cid` FOREIGN KEY (`cid`) REFERENCES `company` (`cid`)
)
COLLATE='latin1_swedish_ci'
ENGINE=InnoDB
;

company和emp是一对多的关系
2.通过帮助文档，建立核心MyBatis配置文件generator.xml,
在该文件中已经告诉MyBatis所链接的数据库，所使用哪种方式对数据表进行映射。以及一些其他信息。

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE generatorConfiguration PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN" "http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">
<generatorConfiguration>
    <!-- 数据库驱动包位置 -->
    <!-- <classPathEntry location="C:\Users\fangjiejie\.IntelliJIdea2016.1\config\jdbc-drivers\mysql-connector-java-5.1.35.jar" /> -->
    <classPathEntry location="C:\Users\fangjiejie\.IntelliJIdea2016.1\config\jdbc-drivers\mysql-connector-java-5.1.35-bin.jar" />
    <context id="mysqltools" targetRuntime="MyBatis3">
        <commentGenerator>
            <property name="suppressAllComments" value="true" />
        </commentGenerator>
        <!-- 数据库链接URL、用户名、密码 -->
        <!-- <jdbcConnection driverClass="com.mysql.jdbc.Driver" connectionURL="jdbc:mysql://localhost:3306/sy" userId="sypro" password="sypro"> -->
        <jdbcConnection driverClass="org.gjt.mm.mysql.Driver" 
            connectionURL="jdbc:mysql://127.0.0.1/test?useUnicode=true&amp;characterEncoding=utf-8" 
            userId="root" password="******">
        </jdbcConnection>
        <javaTypeResolver>
            <property name="forceBigDecimals" value="false" />
        </javaTypeResolver>
        <!-- 生成模型的包名和位置 -->
        <javaModelGenerator targetPackage="com.lyf.model" 
            targetProject="D:\web\mybitsUse">
            <property name="enableSubPackages" value="true" />
            <property name="trimStrings" value="true" />
        </javaModelGenerator>
        <!-- 生成的映射文件包名和位置 -->
        <sqlMapGenerator targetPackage="com.lyf.mapping" 
            targetProject="D:\web\mybitsUse">
            <property name="enableSubPackages" value="true" />
        </sqlMapGenerator>
        <!-- 生成DAO的包名和位置 -->
        <javaClientGenerator type="ANNOTATEDMAPPER" targetPackage="com.lyf.mapper" 
                targetProject="D:\web\mybitsUse">
            <property name="enableSubPackages" value="true" />
        </javaClientGenerator>
        <!-- 要生成那些表(更改tableName和domainObjectName就可以)
            更复杂的方式如下： 但基本不常用
            <table tableName="tmenu" domainObjectName="Menu" enableCountByExample="false" enableUpdateByExample="false" enableDeleteByExample="false" enableSelectByExample="false" selectByExampleQueryId="false" />

        -->
        <table tableName="company" domainObjectName="Company"  />
        <table tableName="emp" domainObjectName="Emp"  />
        <table tableName="user" domainObjectName="User"  />
    </context>
</generatorConfiguration>

3.将generator.xml文档和mybatis的jar 置于某个目录下，本例目录为：D:\web\mybitsUse
4.由java命令生成model,mappper
命令为：java -jar mybatis-generator-core-1.3.2.jar -configfile generator.xml -overwrite

就会在当前目录下生成我们需要的目录com

5.建立一个maven项目
在pom.xml中要加入jar包

    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.31</version>
    </dependency>
        <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.4.1</version>
    </dependency>

6.将我们建立好的com目录移到maven项目中，
7.建立好resources下的资源配置文档mybatis.cfg.xml
注意标清链接的数据库，mapper映射之类

<?xml version="1.0" encoding="UTF-8" ?>     
<!DOCTYPE configuration PUBLIC      
    "-//mybatis.org//DTD Config 3.0//EN"     
    "http://mybatis.org/dtd/mybatis-3-config.dtd">     

<configuration>    

    <environments default="development">     

        <environment id="development">     

            <transactionManager type="JDBC" />     

            <dataSource type="POOLED">     

              <property name="driver" value="org.gjt.mm.mysql.Driver" />     

              <property name="url" value="jdbc:mysql://127.0.0.1/test?useUnicode=true&amp;characterEncoding=utf-8" />    

              <property name="username" value="root" />     

              <property name="password" value="******" />

            </dataSource>     

        </environment>     

    </environments>     
     <mappers>
         <mapper class="com.lyf.mapper.CompanyMapper"/>
         <mapper class="com.lyf.mapper.EmpMapper"/>
         <mapper class="com.lyf.mapper.UserMapper"/>

    </mappers>  


    </configuration>  

8.整个项目的目录结构就建立好了
9.下面实现单表操作的增删改查

package com.lyf.service;

import com.lyf.model.User;
import com.lyf.model.UserExample;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import java.util.List;

/**
 * Created by fangjiejie on 2017/5/29.
 */
public class UserServiceImp {
    SqlSessionFactory ssf;

    public UserServiceImp() {
        ssf=new SqlSessionFactoryBuilder().build(this.getClass().getClassLoader().getResourceAsStream("mybatis.cfg.xml"));
    }

    public static void main(String[] args) {
        new UserServiceImp();
    }
@Test
    public void add(){
        SqlSession sqlSession=ssf.openSession();
        User user=new User();
        user.setUsername("lyf");
        user.setPsw("hahaha");
        sqlSession.insert("com.lyf.mapper.UserMapper.insert",user);
        sqlSession.commit();
        sqlSession.close();
    }
    @Test
    public void del(){
        SqlSession sqlSession=ssf.openSession();
        User user=new User();
        user.setId(8);
        sqlSession.delete("com.lyf.mapper.UserMapper.deleteByPrimaryKey",user);
        //sqlSession.delete("com.lyf.mapper.UserMapper.deleteByPrimaryKey",8);
        sqlSession.commit();
        sqlSession.close();
    }
    @Test
    public void Update(){
        SqlSession sqlSession=ssf.openSession();
        User user=new User();
        user.setId(11);
        user.setUsername("hahahaaa");
        sqlSession.update("com.lyf.mapper.UserMapper.updateByPrimaryKeySelective",user);
        sqlSession.commit();
        sqlSession.close();
    }
    @Test
    public void selectUser(){
        SqlSession sqlSession=ssf.openSession();
        UserExample userExample=new UserExample();
        userExample.createCriteria().andUsernameLike("l%");
        List<User> list= sqlSession.selectList("com.lyf.mapper.UserMapper.selectByExample",userExample);
        for(User u:list){
            System.out.println(u.getUsername());
        }
        sqlSession.close();
    }
}

10.下面演示主从表一对多，多对一的查询
1.在Company类中添加属性对象elist（emp的集合），并作getter和setter

 private Object elist;

    public Object getElist() {
        return elist;
    }

    public void setElist(Object elist) {
        this.elist = elist;
    }

在Emp类中添加对象属性comp(company),并做getter和setter

private Object comp;

    public Object getComp() {
        return comp;
    }

    public void setComp(Object comp) {
        this.comp = comp;
    }

2.在mapper中添加修改映射关系，添加映射方法
CompanyMapper类

修改：
    @Select({
        "select",
        "cid, name, address, pro, city, price",
        "from company",
        "where cid = #{cid,jdbcType=INTEGER}"
    })
    @Results({
        @Result(column="cid", property="cid", jdbcType=JdbcType.INTEGER, id=true),
        @Result(column="name", property="name", jdbcType=JdbcType.VARCHAR),
        @Result(column="address", property="address", jdbcType=JdbcType.VARCHAR),
        @Result(column="pro", property="pro", jdbcType=JdbcType.VARCHAR),
        @Result(column="city", property="city", jdbcType=JdbcType.VARCHAR),
        @Result(column="price", property="price", jdbcType=JdbcType.REAL),
        @Result(property="elist",javaType = List.class,column="cid",
                many = @Many(select="com.lyf.mapper.EmpMapper.selectEmpByCom"))
    })
    Company selectByPrimaryKey(Integer cid);
添加selectComByEmp方法：

    @Select({
            "select",
            "cid, name, address, pro, city, price",
            "from company",
            "where cid = #{cid,jdbcType=INTEGER}"
    })
    @Results({
            @Result(column="cid", property="cid", jdbcType=JdbcType.INTEGER, id=true),
            @Result(column="name", property="name", jdbcType=JdbcType.VARCHAR),
            @Result(column="address", property="address", jdbcType=JdbcType.VARCHAR),
            @Result(column="pro", property="pro", jdbcType=JdbcType.VARCHAR),
            @Result(column="city", property="city", jdbcType=JdbcType.VARCHAR),
            @Result(column="price", property="price", jdbcType=JdbcType.REAL)
              })
    Company selectComByEmp(Integer cid);

EmpMapper类：

修改：
    @Select({
        "select",
        "eid, name, sex, email, salary, cid",
        "from emp",
        "where eid = #{eid,jdbcType=INTEGER}"
    })
    @Results({
        @Result(column="eid", property="eid", jdbcType=JdbcType.INTEGER, id=true),
        @Result(column="name", property="name", jdbcType=JdbcType.VARCHAR),
        @Result(column="sex", property="sex", jdbcType=JdbcType.VARCHAR),
        @Result(column="email", property="email", jdbcType=JdbcType.VARCHAR),
        @Result(column="salary", property="salary", jdbcType=JdbcType.REAL),
        @Result(column="cid", property="cid", jdbcType=JdbcType.INTEGER),
            @Result(property = "comp",column="cid",
            one = @One(select="com.lyf.mapper.CompanyMapper.selectComByEmp"))
    })
    Emp selectByPrimaryKey(Integer eid);

添加selectEmpByCom方法：
    @Select({
            "select",
            "eid, name, sex, email, salary, cid",
            "from emp",
            "where cid = #{cid,jdbcType=INTEGER}"
    })
    @Results({
            @Result(column="eid", property="eid", jdbcType=JdbcType.INTEGER, id=true),
            @Result(column="name", property="name", jdbcType=JdbcType.VARCHAR),
            @Result(column="sex", property="sex", jdbcType=JdbcType.VARCHAR),
            @Result(column="email", property="email", jdbcType=JdbcType.VARCHAR),
            @Result(column="salary", property="salary", jdbcType=JdbcType.REAL),
            @Result(column="cid", property="cid", jdbcType=JdbcType.INTEGER)
    })
    List<Emp> selectEmpByCom(Integer cid);

测试代码：

package com.lyf.service;

import com.lyf.model.Company;
import com.lyf.model.Emp;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import java.util.List;

/**
 * Created by fangjiejie on 2017/5/29.
 */
public class CompanyServiceImp {
    private SqlSessionFactory ssf;
    public CompanyServiceImp(){
        ssf= new SqlSessionFactoryBuilder().build(this.getClass().getClassLoader().getResourceAsStream("mybatis.cfg.xml"));
    }
    @Test
    public void queryEmpByCompany(){
        SqlSession session=ssf.openSession();
        Company company=new Company();
        company.setCid(1);
        Company company1=session.selectOne("com.lyf.mapper.CompanyMapper.selectByPrimaryKey",company);
        List<Emp> list=(List<Emp>)company1.getElist();
        for(Emp e:list){
            System.out.println(e.getName());
        }
        session.close();
    }
 //运行结果：
  MIKE
  JACK
    @Test
    public void queryComByEmp(){
        SqlSession session=ssf.openSession();
        Emp emp1=session.selectOne("com.lyf.mapper.EmpMapper.selectByPrimaryKey",4);
        List<Company> company=(List<Company>) emp1.getComp();
        System.out.println(company.get(0).getName());
        session.close();
    }

}
//运行结果：
京东