Automatic JPA refresh ManyToOne objects with #Version feature - spring-boot

Question

I'm getting an exception:
org.hibernate.TransientPropertyValueException:
object references an unsaved transient instance
- save the transient instance before flushing :
com.example.jpamapstruct.entity.Member.club ->
com.example.jpamapstruct.entity.Club
while saving the member entity:
#Transactional
public MemberDto save(MemberDto memberDto){
Member entity = memberMapper.toEntity(memberDto);
return memberMapper.toDto(repository.save(entity));
}
How to fix this case in a proper way?
Possible solution:
I can get and set a club object before saving a member but is it only one and the best approach in such scenario?
Member entity = memberMapper.toEntity(memberDto);
clubRepository.getReferencedById(memberDto.getClubId()).ifPresent(entity::setClub);
return memberMapper.toDto(repository.save(entity));
Questions:
Should I put this getReferencedById code explicity? I mean what if we have several child objects (unidirectional ManyToOne), for each we need to get data from DB.
Is there any way to handle this by JPA (Spring Data/JPA) "automatically"?
Maybe it is possible to hit DB only one time with f.e join fetch somehow for all childs (with using custom #Query or querydsl or criteria/specification)?
Next, hoow to handle collections (unidirectional manyToMany)? In my case set of events in member object. Also need to loop thru and get all objects one by one before saving member?
Where should I put such logic in a service or maybe better in a mapstuct mapper?
If so, how to use repositories in such mapper?
#Mapper(componentModel = "spring")
public interface MemberMapper extends EntityMapper<MemberDto, Member> {
#AfterMapping
default void afterMemberMapping(#MappingTarget Member m, MemberDto dto) {
var club = clubRepo.findById(m.getClub().getId())
m.setClub(club)
}
Source code:
#Entity
public class Club extends AbstractEntity {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id", nullable = false)
private Long id;
}
public class ClubDto extends AbstractDto {
private Long id;
}
#Entity
public class Member {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id", unique = true, nullable = false)
private Long id;
// commented out as don't want to save child object as it should already exist
// #ManyToOne(cascade = CascadeType.ALL)
#ManyToOne
Club club;
#ManyToMany
#JoinTable(name = "member_events",
joinColumns = #JoinColumn(name = "member_id"),
inverseJoinColumns = #JoinColumn(name = "event_id")
)
List<Event> events = new ArrayList<>();
}
public class MemberDto {
private Long id;
private ClubDto club;
}
#MappedSuperclass
public abstract class AbstractEntity {
#Version
private Integer version;
}
public abstract class AbstractDto {
private Integer version;
}
//MemberMapper above