如何在服务层中以与 Hibernate + JPA 持久化的方法相同的方法检索服务层中持久化 object 的 ID？

Question

I have a Learner object that sign-up to one or multiple Courses. Learner table has a relation one-to-many with LearnerSubmittedToCourse. In my repository, I save the Learner object in PostgreSql, but after, when I try to find the id of Lerner as to send in LearnerSubmittedToCourse table, I cannot access it (or it is not already perssited).

learner1 object should contain the current learner id but it dosent.

OBS. The Learner id is auto-generated in db.! Learner obj doesent contain the id.

My Service:

@Override
public LearnerDto createLearner(LearnerDto learnerDto) {
    Optional<Domain> domain = domainRepository.findById(learnerDto.getDomain().getId());
    Optional<WorkExperience> workExperience = workExperienceRepository.findById(learnerDto.getDomain().getId());
    domain.ifPresent(d -> {
        workExperience.ifPresent(w -> {
            Learner learner = new Learner()
                    .setFirstName(learnerDto.getFirstName())
                    .setLastName(learnerDto.getLastName())
                    .setMobileNo(learnerDto.getMobileNo())
                    .setEmail(learnerDto.getEmail())
                    .setLastJob(learnerDto.getLastJob())
                    .setJob(learnerDto.getJob())
                    .setLearnerDateCreated(learnerDto.getLearnerDateCreated())
                    .setLearnerDetails(learnerDto.getLearnerDetails())
                    .setWhereYouFindUs(learnerDto.getWhereYouFindUs())
                    .setIsCareer(learnerDto.getIsCareer())
                    .setIsBusiness(learnerDto.getIsBusiness())
                    .setObservation(learnerDto.getObservation())
                    .setIsGDPRAccepted(learnerDto.getIsGDPRAccepted())
                    .setScheduledCoursesList(foundScheduledCoursesList)
                    .setDomain(d)
                    .setWorkExperience(w);
            learnerRepository.save(learner);
            Learner learner1 = learnerRepository.findById(learnerDto.getId());

            for (ScheduledCourses course : learnerDto.getScheduledCoursesList()
            ) {
                Optional<ScheduledCourses> foundCourse = scheduledCoursesRepository.findById(course.getId());
                foundCourse.ifPresent(c -> {
                    learnerSubmittedToCourseService.registerLearnerToScheduledCourse(learner1, course);
                });
            }
        });
    });
    return learnerDto;
}

public void registerLearnerToScheduledCourse(Learner learner, ScheduledCourses scheduledCourses) {
Optional<Learner> foundLearner = learnerRepository.findById(learner.getId());
Optional<ScheduledCourses> foundScheduledCourse = scheduledCoursesRepository.findById(scheduledCourses.getId());
foundLearner.ifPresent(l -> {
    foundScheduledCourse.ifPresent(c -> {
        LearnerSubmittedToCourse learnerSubmittedToCourse = new LearnerSubmittedToCourse()
                .setLearner(l)
                .setScheduledCourses(c);
        learnersSubmittedToCourseRepository.save(learnerSubmittedToCourse);
    });
});

How can I get my Learner id as to use it in LearnerSubmittedToCourse object?

Answer 1

learnerRepository.save(learner); is returning the instance you are looking for.

learner = learnerRepository.save(learner); Now the id should be set correctly on learner .

Answer 2

Be aware that in the service code you posted as part of your question, you create and save a new Learner from the info in the DTO. However, the ID which is generated during the save is set on the entity and not on the DTO, so the following call cannot work:

Learner learner1 = learnerRepository.findById(
          learnerDto.getId() // <-- the DTO does not know about the generated ID
                    );