老师，useGeneratedKeys = true
应该就是指定生成的主键回填到入参的coffee的id中吧，我验证了一下，我用的是mysql8，在没指定keyProperty="id",keyColumn="id"时，貌似也不会回填，不知道是不是数据库的问题呢，还是因为我用了druid的数据源？
然后那个save方法的返回值，应该不是id吧，而是操作的记录数，所以我看到有同学评论一直放回1，我也验证过，应该是数量吧，update和delete时返回参数Long对应也是记录操作数？
是这样吗？

回复Francis_Lee:

可以在mapping映射文件中如下定义,userColumns和userJoins就是可以重用的了:

 <sql id="userColumns">
        a.id,
        a.company_id AS "company.id",
        a.office_id AS "office.id",
        a.login_name,
        a.password,
        a.name,
        c.name AS "company.name",
        c.parent_id AS "company.parent.id",
        c.parent_ids AS "company.parentIds",
        ca.id AS "company.area.id",
        ca.name AS "company.area.name",
        ca.parent_id AS "company.area.parent.id",
        ca.parent_ids AS "company.area.parentIds",
        o.name AS "office.name",
        o.parent_id AS "office.parent.id",
        o.parent_ids AS "office.parentIds",
        oa.id AS "office.area.id",
        oa.name AS "office.area.name",
        oa.parent_id AS "office.area.parent.id",
        oa.parent_ids AS "office.area.parentIds",
        cu.id AS "company.primaryPerson.id",
        cu.name AS "company.primaryPerson.name",
        cu2.id AS "company.deputyPerson.id",
        cu2.name AS "company.deputyPerson.name",
        ou.id AS "office.primaryPerson.id",
        ou.name AS "office.primaryPerson.name",
        ou2.id AS "office.deputyPerson.id",
        ou2.name AS "office.deputyPerson.name"
    </sql>
    
    <sql id="userJoins">
        LEFT JOIN sys_office c ON c.id = a.company_id
        LEFT JOIN sys_area ca ON ca.id = c.area_id
        LEFT JOIN sys_office o ON o.id = a.office_id
    </sql>
    
    <select id="get" resultType="User">
        SELECT
            <include refid="userColumns"/>
        FROM sys_user a
        <include refid="userJoins"/>
        WHERE a.id = #{id}
    </select>

官方解释:

sql 这个元素可以被用来定义可重用的 SQL 代码段，可以包含在其他语句中。它可以被静态地(在加载参数) 参数化. 不同的属性值通过包含的实例变化.

丁老师，请教一下，为啥我的接口没有添加@Mapper注解，接口也实例化了，能够执行

public interface UserMapper {
    
    @Select("select * from user_info where id = #{id}")
    User getUserById(@Param("id") int id);
}

@PropertySource(value = {"classpath:config/db.properties"})
@Configuration
public class MyBatisConfig {
    
    @Value("${jdbc.driver}")
    private String driver;
    @Value("${jdbc.url}")
    private String url;
    @Value("${jdbc.username}")
    private String username;
    @Value("${jdbc.password}")
    private String password;
    
    @Bean
    public DriverManagerDataSource dataSource() {
        DriverManagerDataSource dataSource = new DriverManagerDataSource();
        dataSource.setDriverClassName(driver);
        dataSource.setUrl(url);
        dataSource.setUsername(username);
        dataSource.setPassword(password);
        return dataSource;
    }
    
    @Bean
    public SqlSessionFactory sqlSessionFactory() throws Exception {
        SqlSessionFactoryBean factoryBean = new SqlSessionFactoryBean();
        factoryBean.setDataSource(dataSource());
        return factoryBean.getObject();
    }
    
    @Bean
    public MapperFactoryBean<UserMapper> userMapper() throws Exception {
        MapperFactoryBean<UserMapper> factoryBean = new MapperFactoryBean<>(UserMapper.class);
        factoryBean.setSqlSessionFactory(sqlSessionFactory());
        return factoryBean;
    }

}

@ContextConfiguration(classes = {MyBatisConfig.class})
@Slf4j
public class UserTest extends AbstractTestNGSpringContextTests {
    
    @Resource
    private UserMapper userMapper;
    
    @Test(description = "测试MyBatis")
    public void myBatisTest() {
        log.info(userMapper.getUserById(1).toString());
    }
}

老师你好，请问一下，
1.项目运行报了java.lang.IllegalStateException: Type handler was null on parameter mapping for property 'price'. It was either not specified and/or could not be found for the javaType (org.joda.money.Money) : jdbcType (null) combination.
我在网上查找了说应该在typehandler加上javatype和jdbctype，但是加了还是报错，请问这是为什么呢？
2.Mapper没有注入进来，但是MapperScann已经配置了
具体代码：
（1）MybatisDemoApplication .java
@SpringBootApplication
@Slf4j
@MapperScan("ack.mybatisdemo.mapper")
public class MybatisDemoApplication implements ApplicationRunner {

    @Autowired
    private CoffeeMapper coffeeMapper;

    public static void main(String[] args) {
        SpringApplication.run(MybatisDemoApplication.class, args);
    }

    @Override
    public void run(ApplicationArguments args) throws Exception {
        Coffee c = Coffee.builder().name("espresso")
                .price(Money.of(CurrencyUnit.of("CNY"), 20.0)).build();
        int count = coffeeMapper.insert(c);//返回存入条数
        log.info("save coffee-count:{}",count);
        Coffee coffee1 = coffeeMapper.findById(c.getId());
        log.info("coffee,{}",coffee1.toString());
    }
}
（2）handler上面加了
@MappedJdbcTypes(value = JdbcType.BIGINT,includeNullJdbcType = true)
@MappedTypes(Money.class)
（3）mapper类
ack.mybatisdemo.mapper.CoffeeMapper

师傅领进门,修行在个人.老师讲的内容,起到给我拓展知识面的作用,提升我的广度.但是深度还得靠自己.
JPA自己去官网看看手册.结合老师的例子,希望能有提升.
 https://docs.spring.io/spring-data/jpa/docs/2.1.5.RELEASE/reference/html/

当然,作为小白,也希望老师能讲的细一点 :-) ,很多内容希望不要默认我会啊,简单提一下啊,也许会让我醍醐灌顶..