MyBatis-Plus 注解方式（一对多、多对一）

@Repository
public interface UserMapper extends BaseMapper<User> {
  //多对一
    @Results(value = {
            @Result(property = "id", column = "id"),
            @Result(property = "name", column = "name"),
            @Result(property = "age", column = "age"),
            @Result(property = "email", column = "email"),
            @Result(property = "dept", column = "deptid", one = @One(select = "com.atguigu.mybatisplus.mapper.DeptMapper.selectById")),
    })
    @Select("select id, name, age, email, deptid from t_user")
    List<UserVO> getUserDept();
    @Select("select id, name, age, email from t_user where deptid=#{deptid}")
    List<User> getUserByDeptId(@Param("deptid") int deptid);
}

public interface DeptMapper extends BaseMapper<Dept> {
  //一对多
    @Results(value = {
            @Result(property = "id", column = "id"),
            @Result(property = "name", column = "name"),
            @Result(property = "users", column = "id", many = @Many(select = "com.atguigu.mybatisplus.mapper.UserMapper.getUserByDeptId")),
    })
    @Select("select id, name from t_dept")
    List<DeptVO> getDeptUser();
}

@Data
public class DeptVO {
    private Integer id;
    private String name;
    private List<User> users;
}

@Data
public class UserVO {
    private int id;
    private String name;
    private int age;
    private String email;
    private Dept dept;
}

@SpringBootTest
class MybatisplusApplicationTests {
    @Resource
    private IUserService userService;
    @Resource
    private IDeptService deptService;
    @Test
    void contextLoads() {
        List<UserVO> userDept = userService.getUserDept();
        userDept.forEach(System.out::println);
        List<DeptVO> deptUser = deptService.getDeptUser();
        deptUser.forEach(System.out::println);
    }
}