仅在多对多 Hibernate 中插入

Question

我有 2 个表（用户和公告），现在可以将更多用户分配给一个公告（关系是多对多的）， 在我的控制器中，我有：

@Autowired
private AnnouncementService announcementService;

    User user = (User) httpSession.getAttribute("userAccount");
    Announcement announcement = announcementService.getAnnouncement(announcementId);
    user.getAssignedUsersToAnnouncement().add(announcement);
    announcement.getAnnouncementsAssignedToUsers().add(user);

我不想在我的数据库中再次保存这些对象，我只想将关系保存在我的第三个对象（“Assigned_Users”）中。 现在要坚持下去，我应该这样做：

announcementService.save(announcement); //due to this will be dublicates in my table

---

Announcement class{
   @ManyToMany(fetch = FetchType.EAGER)
   @JoinTable(name = "Assigned_Users",
           joinColumns = {@JoinColumn(name = "anunt_id")},
            inverseJoinColumns = {@JoinColumn(name = "user_id")} )
   private Set<User> announcementsAssignedToUsers = new HashSet<User>();
}

---

@ManyToMany(fetch = FetchType.EAGER)
@JoinTable(name = "Assigned_Users",
        joinColumns =  {@JoinColumn(name = "user_id")},
        inverseJoinColumns = {@JoinColumn(name = "anunt_id")})
private Set<Announcement> assignedUsersToAnnouncement = new HashSet<Announcement>();

我得到的用户和公告已经在数据库中，我不想再次保存它们。我怎样才能解决这个问题，并在多对多表中插入

Answer 1

首先，您只需要将关系的 ope 侧映射到@JoinTable。另一方面，您只需要设置mappedBy 属性。所以你的关系看起来像这样

@ManyToMany(fetch = FetchType.EAGER)
@JoinTable(name = "Assigned_Users",
       joinColumns = {@JoinColumn(name = "anunt_id")},
        inverseJoinColumns = {@JoinColumn(name = "user_id")} )
private Set<User> announcementsAssignedToUsers = new HashSet<User>();


@ManyToMany(fetch = FetchType.EAGER, mappedBy = "announcementsAssignedToUsers")
private Set<Announcement> assignedUsersToAnnouncement = new HashSet<Announcement>();

其次，这种类型的逻辑应该在服务类中，而不是在控制器中。从控制器您应该只将 id 传递给服务方法，然后通过服务类中的 id 获取所需的实体。像这样的

// controller
@Autowired
private AnnouncementService announcementService;

    announcementService.assignUserToAnnouncement(user.getId(), annoucmentId);

// service

@Transactional
public void assignUserToAnnouncement(Long userId, Long announcementId) {
    User user = userRepository.getById(userId);
    Announcement announcement = annRepository.getById();
    user.getAssignedUsersToAnnouncement().add(announcement);
    announcement.getAnnouncementsAssignedToUsers().add(user);
    annRepository.save(announcement);
    userRepository.save(user);
}