小编hel*_*llo的帖子

我有双向关系设置如下:

class Child{
    @ManyToOne
    @JoinTable(name = "CHILDREN_WITH_PARENT", 
            joinColumns = {@JoinColumn(name = "CHILD_ID")}, 
            inverseJoinColumns = {@JoinColumn(name = "PARENT_ID")}
    )
    private Parent parent;
}

class Parent{
    @OneToMany(mappedBy="parent", cascade=CascadeType.ALL)
    Set<Child> childrens = new HashSet<Child>();

    public void persistOrMerge() {
        EntityManager em = entityManager();
        em.getTransaction().begin();
        try {
            if (em.contains(this))
                return;
            if (id == null || id == 0) {
                this.setCreatedDate(new Date());
                em.persist(this);
            } else {
                Parent prev = em.find(Parent.class, this.id);
                if (prev == null) {
                    em.persist(this);
                } else{
                    this.setCreatedDate(new Date());
                    em.merge(this);
                }
            }
            em.flush();
            em.getTransaction().commit(); …