I read <https://vladmihalcea.com/the-best-way-to-map-a-onetoone-relationship-with-jpa-and-hibernate/>.
I tried suggestion config like(using spring data JPA,hibernate 5.0 as vendor ):

```
public class PaperSubjectType{
    @Id
    private Long id;

    @OneToOne(fetch = FetchType.LAZY)
    @MapsId
    private PaperSetting paperSetting;
..
}

class PaperSetting{
  @Id
  @GeneratedValue
  private Long id;
..
}

```

first I tried the example:

```
PaperSetting paperSettingInDb = paperSettingRepository.findOne(1);
PaperSubjectType paperSubjectType = new PaperSubjectType();
paperSubjectType.setSubjectCode("91");
paperSubjectType.setPaperSetting(paperSettingInDb);

paperSubjectTypeRepository.save(paperSubjectType);

```

error:detached entity passed to persist:PaperSetting.
it seems hibernate take PaperSetting as detached when cascade 

2 if I want to create both PaperSubjectType and PaperSetting together,do I need to do this:

```
PaperSetting paperSetting = new PaperSetting();
paperSetting.setxx;
PaperSetting  paperSettingInDbNew = paperSettingRepository.save(paperSetting);
PaperSubjectType paperSubjectType = new PaperSubjectType();
paperSubjectType.setPaperSetting(paperSettingInDbNew);
paperSubjectTypeRepository.save(paperSubjectType);

```

or I should use bidirectional in this situation?
thank you！