Mybatis 中如何将sql执行结果封装为目标对象并返回的？都有哪些映射形式？ - 面试宝典

xmlCopy code<select id="selectUser" resultType="com.example.User">
  SELECT * FROM user WHERE id = #{id}
</select>

xmlCopy code<resultMap id="userMap" type="com.example.User">
  <id property="id" column="id"/>
  <result property="name" column="name"/>
  <result property="age" column="age"/>
</resultMap>
<select id="selectUser" resultMap="userMap">
  SELECT * FROM user WHERE id = #{id}
</select>

javaCopy code@Results({
  @Result(property = "id", column = "id"),
  @Result(property = "name", column = "name"),
  @Result(property = "age", column = "age")
})
@Select("SELECT * FROM user WHERE id = #{id}")
User selectUserById(int id);

javaCopy codepublic class User {
    private int id;
    private String name;
    private int age;
    
    // 省略getter和setter方法
}

xmlCopy code<!-- 配置命名空间 -->
<mapper namespace="com.example.UserMapper">
    <!-- 使用resultType将结果映射为User对象 -->
    <select id="selectUser" resultType="com.example.User">
        SELECT * FROM user WHERE id = #{id}
    </select>
    <!-- 使用resultMap定义映射关系将结果映射为User对象 -->
    <resultMap id="userMap" type="com.example.User">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="age" column="age"/>
    </resultMap>
    <select id="selectUserWithMap" resultMap="userMap">
        SELECT * FROM user WHERE id = #{id}
    </select>
</mapper>

javaCopy codepublic interface UserMapper {
    User selectUser(int id);
    User selectUserWithMap(int id);
}

javaCopy code@Configuration
@MapperScan("com.example.mapper")
public class MybatisConfig {
    
    @Bean
    public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
        SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean();
        sessionFactory.setDataSource(dataSource);
        return sessionFactory.getObject();
    }
    
    @Bean
    public MapperScannerConfigurer mapperScannerConfigurer() {
        MapperScannerConfigurer scannerConfigurer = new MapperScannerConfigurer();
        scannerConfigurer.setBasePackage("com.example.mapper");
        return scannerConfigurer;
    }
    
    // 省略其他配置
}

javaCopy code@Autowired
private UserMapper userMapper;
public void getUser() {
    // 使用resultType方式
    User user = userMapper.selectUser(1);
    System.out.println(user.getId() + " - " + user.getName() + " - " + user.getAge());
    
    // 使用resultMap方式
    User userWithMap = userMapper.selectUserWithMap(1);
    System.out.println(userWithMap.getId() + " - " + userWithMap.getName() + " - " + userWithMap.getAge());
}