Mybatis 不同使用方式

前言

工作这么多年，ORM框架一直选择Mybatis框架。 Mybatis的使用方式也一直在变，总体来说是越来越简单。写篇文章对各使用方式做个总结...

正文

一、Mybatis典型用法

1. 正常执行流程

♦  配置文件 - 全局配置信息和映射文件信息。全局配置信息包括：数据库配置和事务配置。映射文件就是SQL相关的

♦  Mybatis读取配置文件生成SqlSessionFactory，即回话工厂

♦  获取SqlSession, 做CRUD操作。但真正做这个事情的是底层的executor。

♦  Executor执行器把SQL分装到MappedStatement对象中。该对象包括：SQL, 输入参数映射信息和输出结果映射信息。

2. 案例

2.1 建表

CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `username` varchar(20) ,
  `password` varchar(20) ,
  `age` int(11) ,
  PRIMARY KEY (`id`)
)

2.2 全局配置文件

<?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="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3307/book"/>
        <property name="username" value="root"/>
        <property name="password" value="root"/>
      </dataSource>
    </environment>
  </environments>
  <mappers>
    <mapper resource="mybatis/User.xml"/>
  </mappers>
</configuration>

2.3 mapper.xml

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

<mapper namespace="user">
  <select id="findUserById" parameterType="int" resultType="com.mybatis.User">
    select * from user where id = #{id}
  </select>
  <select id="findUserAll" resultType="com.mybatis.User">
    select * from user
  </select>
  <insert id="insertUser" parameterType="com.mybatis.User">
    insert into user(username,password,age) values(#{username},#{password},#{age})
  </insert>
  <delete id="deleteUserById" parameterType="int">
    delete from user where id=#{id}
  </delete>
  <update id="updateUserPassword" parameterType="com.mybatis.User">
    update user set password=#{password} where id=#{id}
  </update>
</mapper>

2.4 Dao 接口

package com.mybatis.dao;

import com.mybatis.User;

import java.util.List;

public interface UserDao {
  public User findUserById(int id) throws Exception ;
  public List<User> findAllUsers() throws Exception;
  public void insertUser(User user) throws Exception;
  public void deleteUserById(int id) throws Exception;
  public void updateUserPassword(User user) throws Exception;
}

2.5 DaoImpl

package com.mybatis.dao.impl;

import com.mybatis.User;
import com.mybatis.dao.UserDao;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class UserDaoImpl implements UserDao {
  private static SqlSessionFactory factory = null;
  static {
    String resource = "mybatis/SqlMapConfig.xml";
    InputStream inputStream = null;
    try {
      inputStream = Resources.getResourceAsStream(resource);
    } catch (IOException e) {
      e.printStackTrace();
    }
    factory = new SqlSessionFactoryBuilder().build(inputStream);
  }

  public static SqlSession getSession(){
    return factory.openSession();
  }

  @Override
  public User findUserById(final int id) throws Exception {
    return getSession().selectOne("user.findUserById",id);
  }

  @Override
  public List<User> findAllUsers() throws Exception {
    return null;
  }

  @Override
  public void insertUser(final User user) throws Exception {

  }

  @Override
  public void deleteUserById(final int id) throws Exception {

  }

  @Override
  public void updateUserPassword(final User user) throws Exception {

  }
}

2.6 User类

package com.mybatis;

import lombok.Data;

@Data
public class User {
  private Integer id;
  private String username;
  private String password;
  private Integer age;
}

2.7 测试类

package com.mybatis.dao;

import com.mybatis.User;
import com.mybatis.dao.impl.UserDaoImpl;

import org.junit.Test;

public class UserDaoTest {
  @Test
  public void testFindUserById() throws Exception{
    UserDao userDao = new UserDaoImpl();
    User user = userDao.findUserById(7);
    System.out.println(user);
  }
}

二、Mapper代理开发方式

Mapper代理的开发方式，我们只需要编写mapper接口，不需要再Dao类，MyBatis会为我们生成代理类。代理开发方式应当遵循以下条件：

♦  mapper接口的全限定名要和mapper映射文件的namespace的值相同。

♦  mapper接口的方法名称要和mapper映射文件中的statement的id相同。

♦  mapper接口的方法参数只能有一个，且类型要和mapper映射文件中statement的parameterType的值保持一致。

♦  mapper接口的返回值类型要和mapper映射文件中statement的resultType值或resultMap中的type值保持一致。

案例:

1. 建表 同2.1

2. 全局配置 同2.2

3. mapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--参考四要素-->
<mapper namespace="com.mybatis2.dao.UserDao">
  <select id="findUserById" parameterType="int" resultType="com.mybatis2.User">
    select * from user where id = #{id}
  </select>

<select id="findUserAll" resultType="com.mybatis2.User">

select * from user

</select>
<insert id="insertUser" parameterType="com.mybatis.User">
  insert into user(username,password,age) values(#{username},#{password},#{age})
</insert>
<delete id="deleteUserById" parameterType="int">
  delete from user where id=#{id}
</delete>
<update id="updateUserPassword" parameterType="com.mybatis.User">
  update user set password=#{password} where id=#{id}
</update>

</mapper>

4.mapper类：类名无所谓，用*Dao或者*Mapper都可以

package com.mybatis2.dao;

import com.mybatis2.User;

import java.util.List;

public interface UserDao {

public User findUserById(int id) throws Exception ;
public List<User> findUserAll() throws Exception;
public void insertUser(User user) throws Exception;
public void deleteUserById(int id) throws Exception;
public void updateUserPassword(User user) throws Exception;

}

5. User类同2.5

6. 测试类

package com.mybatis.dao;

import com.mybatis2.dao.UserDao;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.BeforeClass;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;

public class UserDaoTest2 {
  private static SqlSessionFactory factory = null;
  @BeforeClass
  public static void init(){
    String resource = "mybatis/SqlMapConfig.xml";
    InputStream inputStream = null;
    try {
      inputStream = Resources.getResourceAsStream(resource);
    } catch (IOException e) {
      e.printStackTrace();
    }
    factory = new SqlSessionFactoryBuilder().build(inputStream);
  }
  @Test
  public void testFindUserById() throws Exception{
    UserDao mapp = factory.openSession().getMapper(UserDao.class);
    System.out.println(mapp.findUserById(7));
  }
}

　　

三、与Spring框架的集成

相关背景，使用方式官方文档已经很详细了。参考官方文档 -  http://www.mybatis.org/spring/