MyBatis快速入门

思路流程：搭建环境—>导入Mybatis–>编写代码—>测试

1、代码演示

1.1、搭建数据库

CREATE DATABASE `mybatis`;USE `mybatis`;CREATE TABLE `user` (`id` int(20) NOT NULL AUTO_INCREMENT,`username` varchar(50) NOT NULL,`address` varchar(50) NOT NULL,PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;insert  into `user`(`id`,`username`,`address`)
values (1,'詹姆斯','克里夫'),
(2,'科比','洛杉矶'),
(3,'保罗','洛杉矶'),
(4,'苏炳添','中国');

1.2、导入MyBatis相关依赖

<!--导入mybatis依赖--><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.5</version></dependency><!--导入mysql依赖--><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.21</version></dependency><!--单元测试--><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.13</version><scope>test</scope></dependency>

1.3、编写Mybatis核心配置文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><!--配置环境(可以配置多套环境，可以指定选用的环境)--><environments default="development"><!--配置mysql的环境--><environment id="development"><!--配置事务的类型--><transactionManager type="JDBC"/><!--配置数据源(连接池)--><dataSource type="POOLED"><!--配置连接数据库的基本信息--><property name="driver" value="com.mysql.cj.jdbc.Driver"/><property name="url" value="jdbc:mysql://localhost:3306/mybatis?serverTimezone=UTC"/><property name="username" value="root"/><property name="password" value="root"/></dataSource></environment></environments><!--指定映射配置文件的位置--><mappers><mapper resource="mapper/UserMapper.xml"/></mappers>
</configuration>

1.4、编写实体类

package com.lili.entity;/*** 对应数据库下的t_user表** @author: QiJingJing* @create: 2021/8/6*/
public class User {/*** 用户编号*/private int id;/*** 姓名*/private String username;/*** 住址*/private String address;public void setId(int id) {this.id = id;}public User() {}public User(String username, String address) {this.username = username;this.address = address;}public int getId() {return this.id;}public void setUsername(String username) {this.username = username;}public String getUsername() {return this.username;}public void setAddress(String address) {this.address = address;}public String getAddress() {return this.address;}@Overridepublic String toString() {return "User{" +"id=" + id +", username='" + username + '\'' +", address='" + address + '\'' +'}';}
}

1.5、编写Mybatis工具类（获取SqlSession对象）

package com.lili.utils;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;/*** 获取sqlSession对象** @author: QiJingJing* @create: 2021/8/6*/
public class MybatisUtil {private static SqlSessionFactory sqlSessionFactory;static {try {// 获取sqlSessionFactoryInputStream in = Resources.getResourceAsStream("mybatis-config.xml");sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);} catch (IOException e) {e.printStackTrace();}}/*** 获取sqlSession对象*/public static SqlSession getSqlSession() {return sqlSessionFactory.openSession();}
}

1.6、编写Mapper接口类

public interface UserMapper {/*** 查询所有操作*/List<User> findAll();
}

1.7、编写Mapper.xml配置文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapperPUBLIC "-//mapper.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.lili.dao.UserMapper"><!--查询所有信息--><select id="findAll" resultType="com.lili.entity.User">select *from user</select>
</mapper>

1.8、编写测试类

public class MybatisTest {@Testpublic void userDaoTest() {// 放到 try 里面sqlSession会自动关闭try (SqlSession sqlSession = MybatisUtil.getSqlSession()) {// 执行sqlUserMapper mapper = sqlSession.getMapper(UserMapper.class);List<User> userList = mapper.findAll();userList.forEach(System.out::println);} catch (Exception e) {e.printStackTrace();}}
}

1.9、运行测试，结果如下

User{id=1, username='詹姆斯', address='克里夫'}
User{id=2, username='科比', address='洛杉矶'}
User{id=3, username='保罗', address='洛杉矶'}
User{id=4, username='苏炳添', address='中国'}

2、CRUD

2.1、select

select语句的属性
- id
  - 命名空间中唯一标识符
  - 接口中的方法必须与映射文件中的SQL语句ID一一对应
- parameterType
  - 传入SQL的参数类型。【如果参数过多可以使用Map】
- resultType：
  - SQL语句返回值类型。【完整的类名或别名】

需求1：根据id查询用户

1.在UserMapper中添加对应方法

public interface UserMapper {/*** 查询所有操作*/List<User> findAll();/*** 根据id查询用户*/User findById(@Param("id") int id);
}

2.在UserMapper.xml中添加对应select语句

<!--查询根据Id查询用户-->
<select id="findById" parameterType="integer" resultType="com.lili.entity.User">select *from userwhere id = #{id}
</select>

3.测试类中进行测试

   @Testpublic void test2() {// 获取SqlSessiontry (SqlSession sqlSession = MybatisUtil.getSqlSession()) {// 得到UserMapper对象UserMapper mapper = sqlSession.getMapper(UserMapper.class);// 执行查询User user = mapper.findById(1);// 打印System.out.println(user);} catch (Exception e) {e.printStackTrace();}}

4.输出如下

User{id=1, username='詹姆斯', address='克里夫'}

需求2：根据用户名和住址查询用户

方法一：直接在方法中传递参数

在接口方法的参数前加 @Param属性
Sql语句编写的时候，直接取@Param中设置的值即可，不需要单独设置参数类型

User findByUA(@Param("username") String username,@Param("address") String address);<select id="findByUA" resultType="com.lili.entity.User">select *from userwhere username = #{username}and address = #{address}</select>

方法二：使用Map传参

1.在接口方法上，直接使用map参数

User findByMap(Map<String,Object> map);

2.UserMapper.xml

<select id="findByMap" parameterType="map" resultType="com.lili.entity.User">select *from userwhere username = #{username}and address = #{address}
</select>

3.在使用方法的时候,Map的key为sql中取得值即可，没有顺序要求

Map<String,Object> map = new HashMap<>();
map.put("username","苏炳添");
map.put("address","中国");
// 执行查询
User user = mapper.findByMap(map);

2.2、insert

需求：给数据库增加一个用户

1.在UserMapper中添加对应方法

int addUser(User user);

2.UserMapper.xml

 <insert id="addUser" parameterType="com.lili.entity.User">insert into user (`id`, `username`, `address`)values (#{id}, #{username}, #{address})</insert>

3.测试代码

User user = new User();
user.setId(5);
user.setUsername("齐菁菁");
user.setAddress("河南");
// 执行添加
int i = mapper.addUser(user);
System.out.println(i);
// 注意：增删改操作必须提交
sqlSession.commit();

2.3、update

需求：把id为5的地址改为中国

1.在UserMapper中添加对应方法

 int update(@Param("address") String address,@Param("id") int id);

2.UserMapper.xml

 <update id="update" >update userset address = #{address}where id = #{id}</update>

3.测试代码

 UserMapper mapper = sqlSession.getMapper(UserMapper.class);int i = mapper.update("中国", 5);System.out.println(i);// 注意：增删改操作必须提交sqlSession.commit();

2.4、delete

需求：根据id删除一个用户

1.在UserMapper中添加对应方法

int deleteById(@Param("id") int id);

2.UserMapper.xml

<delete id="deleteById" >delete from user where id = #{id}</delete>

3.测试代码

 int i = mapper.deleteById(1);System.out.println(i);// 注意：增删改操作必须提交sqlSession.commit();

小结：

所有的增删改操作都需要提交事务！
接口所有的普通参数，尽量都写上@Param参数，尤其是多个参数时，必须写上！
有时候根据业务的需求，可以考虑使用map传递参数！
为了规范操作，在SQL的配置文件中，我们尽量将Parameter参数和resultType都写上！