Map a dto to an entity retrieved from database if Dto has Id using MapStruct

I'm using MapStruct to make dto <-> entity mapping. The same mappers are used to create and update entities from dtos. A verification of the dto's id is done to know whether a new entity must be created (id == null) or it should be retrieved from database (id != null) .

I'm actually using MapperDecorator as a workaround. Example :

Mapper

@Mapper
@DecoratedWith(UserAccountDecorator.class)
public interface UserAccountMapper {

    UserAccountDto map(User user);

    User map(UserAccountDto dto);

    User map(UserAccountDto dto, @MappingTarget User user);
}

Decorator

public abstract class UserAccountDecorator implements UserAccountMapper {

    @Autowired
    @Qualifier("delegate")
    private UserAccountMapper delegate;

    @Autowired
    private UserRepository userRepository;

    @Override
    public User map(UserAccountDto dto) {
        if (dto == null) {
            return null;
        }

        User user = new User();
        if (dto.getId() != null) {
            user = userRepository.findOne(dto.getId());
        }

        return delegate.map(dto, user);
    }

}

But this solution becomes heavy due to the fact that a decorator must be created for each mapper.

Is there any good solution to perform that ?

---

I'm using :

1. MapStruct : 1.1.0

I solved my problem by following the advice of Gunnar in the comment.

I moved to MapStruct 1.2.0.Beta1 and created a UserMapperResolver like below

@Component
public class UserMapperResolver {

    @Autowired
    private UserRepository userRepository;

    @ObjectFactory
    public User resolve(BaseUserDto dto, @TargetType Class<User> type) {
        return dto != null && dto.getId() != null ? userRepository.findOne(dto.getId()) : new User();
    }

}

Which I use then in my UserMapper :

@Mapper(uses = { UserMapperResolver.class })
public interface BaseUserMapper {

    BaseUserDto map(User user);

    User map(BaseUserDto baseUser);

}

The generated code is now :

@Override
    public User map(BaseUserDto baseUser) {
        if ( baseUser == null ) {
            return null;
        }

        User user = userMapperResolver.resolve( baseUser, User.class );

        user.setId( baseUser.getId() );
        user.setSocialMediaProvider( baseUser.getSocialMediaProvider() );
...
}

Works well !