Mybatis入门笔记

 1.Mybatis简介

1. 什么是Mybatis

• Mybatis是一款优秀的持久层框架
• 支持定制化SQL、存储过程以及高级映射
• 避免了几乎所有的JDBC代码、手动设置参数以及获取结果集

Maven仓库：

<dependency>
    <groupID>org.mybatis</groupID>
    <artifactID>mybatis</artifactID>
    <version>3.5.2</version>
</dependency>

2. 持久化

数据持久化

• 持久化就是将程序的数据在持久状态和瞬时状态转化的过程
• 数据库（jdbc），io文件持久化

3. 持久层

Dao层，Service层，Controller层...

• 完成持久化工作的代码块
• 层界限明显

4. Mybatis的特点

• 简单方便，没有第三方依赖
• 接触sql与程序代码之间的耦合，通过Dao层将业务逻辑和数据访问罗技分离，使系统的设计更清晰，更易维护。
• 提供映射标签，支持对象和数据库的orm字段关系映射
• 提供对象关系映射标签，支持对象关系组建维护
• 提供xml标签，支持编写动态sql

2.第一个Mybatis程序

1. Mybatis思路

搭建环境->导入Mybatis->编写代码->测试

2.搭建环境

• 搭建数据库

CREATE DATABASE `mybatis`;

USE `mybatis`;

CREATE TABLE `user`(
	`id` INT(20) NOT NULL PRIMARY KEY,
	`name` VARCHAR(30) DEFAULT NULL,
	`pwd` VARCHAR(30) DEFAULT NULL
 
)ENGINE=INNODB DEFAULT CHARSET=utf8;

insert into `user` (`id`,`name`,`pwd`)values 
(1,'xx','123'),
(2,'kk','1234'),
(3,'ss','1235')

ENGINE=INNODB DEFAULT CHARSET=utf8 面试常考！！！

3. 新建maven项目

• 删除src目录，作为父工程
• 导入maven依赖
• 以下代码需要添加进pom.xml中，防止后续测试找不到mapper.xml文件

  <build>
      <resources>
          <resource>
          <directory>src/main/resource</directory>
              <includes>
                  <include>**/*.properties</include>
               <include>**/*.xml</include>
              </includes>
              <filtering>false</filtering>
          </resource>
          <resource>
              <directory>src/main/java</directory>
              <includes>
                  <include>**/*.properties</include>
                  <include>**/*.xml</include>
              </includes>
              <filtering>false</filtering>
          </resource>
      </resources>
  </build>

4. 创建模块

• 编写mybatis核心配置文件configuration

<?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.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncodingUTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="org/mybatis/example/BlogMapper.xml"/>
    </mappers>
</configuration>

<property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncodingUTF-8"/>

&amp；相当于&，在xml中转义。防止中文出错等。

• 编写mybatis工具类

//sqlSessionFactory -->sqlSession
public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;

    static {
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

5. 编写代码

• 实体类

package com.wzh.pojo;

//实体类
public class User {
    private int id;
    private String name;
    private String password;

    public User() {
    }

    public User(int id, String name, String password) {
        this.id = id;
        this.name = name;
        this.password = password;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getPassword() {
        return password;
    }

    public void setId(int id) {
        this.id = id;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

• Dao接口

public interface UserDao {
    List<User> getUserList();
}

• 接口实现类由原来的UserDaoImpl转变为一个Mapper配置文件

<?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="com.wzh.dao.UserDao">
<!--    查询语句-->
    <select id="getUserList" resultType="com.wzh.pojo.User">
        select * from mybatis.user
    </select>
</mapper>

6. 测试

在核心配置文件configuration中绑定mapper

<mappers>
    <mapper resource="com/wzh/dao/UserMapper"/>
</mappers>

编写测试类UserDaoTest

public class UserDaoTest {

    @Test
    public void test(){
        //第一步 获得SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        //方式一：getMapper 推荐使用
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        List<User> userList = userDao.getUserList();

        //方式二：不推荐使用
//        List<User> userList = sqlSession.selectList("com.wzh.dao.UserDao.getUserList");

        for (User user : userList) {
            System.out.println(user);
        }

        sqlSession.close();
    }

SqlSession sqlSession = MybatisUtils.getSqlSession();

sqlSession.close();

这两步是固定的，每个Test中复制粘贴即可

3.总结

1.namespace

namespace中的包名要和Dao/Mapper中的包名一致

2.select

        1.编写接口

//查询全部用户
List<User> getUserList();
//根据ID查询用户
User getUserById(int id);

         2.编写对应的mapper中的sql语句

<select id="getUserList" resultType="com.wzh.pojo.User">
    select * from mybatis.user
</select>

<select id="getUserById" parameterType="int" resultType="com.wzh.pojo.User">
    select * from mybatis.user where id = #{id}
</select>

        3.测试

@Test
    public void test(){
        
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        UserDao userDao = sqlSession.getMapper(UserDao.class);
        List<User> userList = userDao.getUserList();
        
        for (User user : userList) {
            System.out.println(user);
        }
        
        sqlSession.close();
    }
    @Test
    public void getUserById(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        //获取需要的接口的class对象
        UserDao mapper = sqlSession.getMapper(UserDao.class);
        User user = mapper.getUserById(1);
        System.out.println(user);

        sqlSession.close();
    }

3. insert

        1.编写接口

//插入用户信息
int addUser(User user);

        2.编写对应mapper中的sql语句

<insert id="addUser" parameterType="com.wzh.pojo.User">
    insert into mybatis.user (id, name, pwd) VALUES (#{id},#{name},#{password})
</insert>

        3.测试

//增删改查需要提交事务
@Test
public void addUser(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();

    UserDao mapper = sqlSession.getMapper(UserDao.class);
    int res = mapper.addUser(new User(4,"heihei","123456"));
    if(res > 0){
        System.out.println("插入成功");
    }

    //提交事务 !!!!!!!
    sqlSession.commit();

    sqlSession.close();

}

增删改查需要提交事务！！！！

3. update

        1.编写接口

//更新用户信息
int updateUser(User user);

        2.编写对应mapper中的sql语句

<update id="updateUser" parameterType="com.wzh.pojo.User">
    update mybatis.user set name=#{name},pwd=#{password} where id=#{id}
</update>

        3.测试

@Test
public void updateUser(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    UserDao mapper = sqlSession.getMapper(UserDao.class);

    mapper.updateUser(new User(4,"wangerxiao","123"));

    sqlSession.commit();
    sqlSession.close();
}

4. delete

        1.编写接口

//删除用户信息
int deleteUser(int id);

        2.编写对应mapper中的sql语句

<delete id="deleteUser" parameterType="com.wzh.pojo.User">
    delete from mybatis.user where id=#{id}
</delete>

        3.测试

@Test
public void deleteUser(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    UserDao mapper = sqlSession.getMapper(UserDao.class);

    mapper.deleteUser(4);

    sqlSession.commit();
    sqlSession.close();
}