Java 多对多协会。数据不'；不删除

我有这个模型：

@Entity
@Table(name = "candidate")
@XmlRootElement(name = "candidate")
public class Candidate{
@ManyToMany(mappedBy = "candidates", fetch = FetchType.EAGER)
    @XmlTransient
    public Set<Vacancy> getVacancies() {
        return vacancies;
    }
....
}

候选人:

@Override
    public boolean update(Candidate candidate) throws HibernateException{
        Session session = sessionFactory.getCurrentSession();
        if (candidate == null) {
            return false;
        }
        session.update(candidate);

        return true;

    }

我有奇怪的行为。如果我给应聘者增加新的职位空缺，效果会很好。但是，如果我删除空缺，这是行不通的

---

这对我来说是不理解的。

当你从候选人名单中删除空缺时，别忘了从空缺名单中删除候选人，反之亦然。还请记住：如果您的系统中有某个位置稍后发送已删除的空缺（反之亦然），则该实体将再次保留

@RequestMapping("/saveCandidate")
public String saveCandidate(
        Model model,
        @ModelAttribute("candidateFromRequest") Candidate candidateFromRequest,

        @ModelAttribute("vacanciesForCandidate") Set<Vacancy> vacanciesForCandidate,

        RedirectAttributes redirectAttributes) {

    candidateService.updateCandidateAndLinkedEntities(candidateFromRequest,
            vacanciesForCandidate,...);
    ...
}

    @Transactional
    @Service("candidateService")
    public class CandidateService {
    public void updateCandidateAndLinkedEntities(Candidate candidate,
                Set<Vacancy> vacancies, ...) {

            if (candidate == null)
                throw new NullPointerException("null candidate entity");


            if (vacancies != null) {

                candidate.setVacancies(vacancies);

                for (Vacancy vacancy : vacancies) {
                    vacancy.getCandidates().add(candidate);
                    vacancyDao.update(vacancy);
                }
            }
            candidateDao.update(candidate);//here all right, how I wish(I am about state of candidate entity)

        }
        ...
    }

@Override
    public boolean update(Vacancy vacancy) throws HibernateException {
        Session session = sessionFactory.getCurrentSession();
        if (vacancy == null) {
            return false;
        }
        session.update(vacancy);
        return true;

    }

@Override
    public boolean update(Candidate candidate) throws HibernateException{
        Session session = sessionFactory.getCurrentSession();
        if (candidate == null) {
            return false;
        }
        session.update(candidate);

        return true;

    }