Java 删除spring MVC中的操作

用户和检查点具有多对多关系。我可以在数据库中保存值，但不能从数据库中删除值

User.java

@Id
@GeneratedValue
private Integer id;
@ManyToMany
Set<Roles> roles;

@ManyToMany(fetch = FetchType.EAGER) 
List<Checkpoints> checkpoints;

public User() {
    super();
}

public Integer getId() {
    return id;
}

public void setId(Integer id) {
    this.id = id;
}

public List<Checkpoints> getCheckpoints() {
    return checkpoints;
}

public void setCheckpoints(List<Checkpoints> checkpoints) {
    this.checkpoints = checkpoints;
}

在我的UserDaoImpl中

@Transactional 
@Override
public User saveUser(User user) {
    // TODO Auto-generated method stub 
    return entityManager.merge(user);
}

请让我知道我做错了什么，或者用其他方法做同样的事情！！

---

提前谢谢

你的许多注释上的级联属性？@NeilMcGuigan感谢你的研究！！我刚找到解决办法！！我正在从user（存储在会话中）而不是userDao中删除检查点对象。

@RequestMapping(value="/checkpointadd.html", method = RequestMethod.POST) 
public void checkpoint(@RequestParam Integer categoryId, HttpSession    session){    // This works fine
    System.out.println("Checkpoint checked :"+categoryId); 
    User user = (User) session.getAttribute("loggeduser");
    Checkpoints cp = userDao.getCheckpointById(categoryId);
    user.getCheckpoints().add(cp);
    userDao.saveUser(user);
    user.getCheckpoints().remove(cp);
}

@RequestMapping(value="/checkpointremove.html", method = RequestMethod.POST) 
public void checkpointremove(@RequestParam Integer categoryId, HttpSession session){   // I'm doing something wrong here
    System.out.println("Checkpoint removed :"+categoryId); 
    User user = (User) session.getAttribute("loggeduser");
    Checkpoints cp = userDao.getCheckpointById(categoryId);
    user.getCheckpoints().remove(cp);
    userDao.saveUser(user);
}

@Transactional 
@Override
public User saveUser(User user) {
    // TODO Auto-generated method stub 
    return entityManager.merge(user);
}