Mybatis学习笔记：Mybatis使用

准备工作

首先新建一张表，用于记录读过的书，有几个简单的字段：

CREATE TABLE `reading_list` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '主键',
  `book_id` bigint(20) NOT NULL COMMENT '书籍ID',
  `start_date` varchar(16) NOT NULL COMMENT '开始日期',
  `end_date` varchar(16) NOT NULL COMMENT '结束日期',
  `deleted` tinyint(4) DEFAULT '0' COMMENT '是否删除',
  `gmt_create` bigint(20) NOT NULL COMMENT '创建时间',
  `gmt_update` bigint(20) NOT NULL COMMENT '更新时间',
  PRIMARY KEY (`id`),
  KEY `idx_gmt_create` (`gmt_create`),
  KEY `idx_gmt_update` (`gmt_update`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='阅读记录';

mybatis配置

接下来写mybatis的配置文件，可以直接从官网上copy：

<?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>
  <settings>
    <setting name="logImpl" value="STDOUT_LOGGING"/>
    <setting name="mapUnderscoreToCamelCase" value="true"/>
  </settings>

  <typeAliases>
    <typeAlias type="org.xinghe.xh.entity.ReadingListEntity" alias="ReadingListEntity"/>
  </typeAliases>

  <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://127.0.0.1:3306/muggle_java"/>
        <property name="username" value="root"/>
        <property name="password" value="root"/>
      </dataSource>
    </environment>
  </environments>

  <mappers>
    <mapper resource="mapper/ReadingListMapper.xml"/>
  </mappers>

</configuration>

这里配置了几个节点：

• settings：节点是调整设置，影响mybatis的运行时行为
• typeAliases：类型别名设置
• environments：mybatis运行环境设置
• mappers：mybatis映射器配置，执行的SQL会在这里找

代码编写

接口类

public interface ReadingListDao {

    int insert(ReadingListEntity readingListEntity);

    List<ReadingListEntity> getList();

    ReadingListEntity getById(Long id);
}

对应的mapper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="org.xinghe.xh.dao.ReadingListDao">

  <insert id="insert">
    insert into reading_list(book_id,start_date,end_date,deleted,gmt_create,gmt_update)
    values(#{bookId},#{startDate},#{endDate},0,#{gmtCreate},#{gmtUpdate})
  </insert>

  <select id="getList" resultType="org.xinghe.xh.entity.ReadingListEntity">
    select * from reading_list where deleted = 0
  </select>

  <select id="getById" resultType="org.xinghe.xh.entity.ReadingListEntity">
    select * from reading_list where deleted = 0 and id = #{id}
  </select>
  
</mapper>

测试

@TestInstance(Lifecycle.PER_CLASS)
class ReadingListDaoTest {

    private ReadingListDao readingListDao;

    @BeforeAll
    void before() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession sqlSession = factory.openSession();
        readingListDao = sqlSession.getMapper(ReadingListDao.class);
    }

    @Test
    void getList() {
        List<ReadingListEntity> list = readingListDao.getList();
        System.out.println("查询结果：" + list);
    }

}

运行结果：

完美通过。

mybatis的使用非常简单，基本上官网上都说完了。如果要使用缓存，也只需要在mapper文件添加一行代码：

<?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="org.xinghe.xh.dao.ReadingListDao">

  <cache type="org.mybatis.caches.ehcache.EhcacheCache"/>

</mapper>

对应的测试：

    @Test
    void getById() {
        ReadingListEntity entity = readingListDao.getById(4L);
        System.out.println("第一次查询" + entity.toString());
        ReadingListEntity second = readingListDao.getById(4L);
        System.out.println("第二次查询" + second.toString());
    }

运行结果：

日志上可以看出，第一次查询未命中缓存，所以查询了数据库；第二次查询命中缓存，直接返回结果。

总结

总的来说，mybatis的使用很简单，参照官网很快就能上手。