java - JPA : removing from a collection 中管理双向关系时出现问题

Question

我的域模型与实体中完成的关系管理具有自引用双向关系:

@Entity
public class Users implements BaseEntity<String>, Serializable {

    @Id
    private String username;
    @ManyToMany(cascade = {CascadeType.REFRESH, CascadeType.MERGE, CascadeType.PERSIST})
    private List<User> associatedSenders;
    @ManyToMany(mappedBy = "associatedSenders")
    private List<User> associatedReceivers;

    //
    // Associated Senders
    //
    public List<User> getAssociatedSenders() {
        if (associatedSenders == null) {
            associatedSenders = new ArrayList<User>();
        }

        return associatedSenders;
    }

    public void addAssociatedSender(User sender) {
        if (associatedSenders == null) {
            associatedSenders = new ArrayList<User>();
        }

        associatedSenders.add(checkNotNull(sender));
        if (!sender.getAssociatedReceivers().contains(this)) {
            sender.addAssociatedReceiver(this);
        }
    }

    public void removeAssociatedSender(User sender) {
        if (associatedSenders == null) {
            associatedSenders = new ArrayList<User>();
        }

        associatedSenders.remove(checkNotNull(sender));
        if (sender.getAssociatedReceivers().contains(this)) {
            sender.removeAssociatedReceiver(this);
        }
    }

    public void setAssociatedSenders(List<User> senders) {
        checkNotNull(senders);

        if (associatedSenders == null) {
            associatedSenders = new ArrayList<User>();
        }

        // first remove all previous senders
        for (Iterator<User> it = associatedSenders.iterator(); it.hasNext();) {
            User sender = it.next();
            it.remove();
            if (sender.getAssociatedReceivers().contains(this)) {
                sender.removeAssociatedReceiver(this);
            }
        }

        // now add new senders
        for (User sender : senders) {
            addAssociatedSender(sender);
        }
    }

    //
    // Associated Receivers
    //
    public List<User> getAssociatedReceivers() {
        if (associatedReceivers == null) {
            associatedReceivers = new ArrayList<User>();
        }

        return associatedReceivers;
    }

    /**
     * <p><b>Note:</b> this method should not be used by clients, because it
     * does not manage the inverse side of the JPA relationship. Instead, use
     * the appropriate method at the inverse of the relationship.
     * 
     * @param receiver
     */
    protected void addAssociatedReceiver(User receiver) {
        if (associatedReceivers == null) {
            associatedReceivers = new ArrayList<User>();
        }

        associatedReceivers.add(checkNotNull(receiver));
    }

    /**
     * <p><b>Note:</b> this method should not be used by clients, because it
     * does not manage the inverse side of the JPA relationship. Instead, use
     * the appropriate method at the inverse of the relationship.
     *
     * @param receiver
     */
    protected void removeAssociatedReceiver(User receiver) {
        if (associatedReceivers == null) {
            associatedReceivers = new ArrayList<User>();
        }

        associatedReceivers.remove(checkNotNull(receiver));
    }
}

当我将新用户实体添加到 linkedSenders 集合时，一切都按预期进行。数据库中的表得到正确更新，内存中的关系也正确。但是，当我从 linkedSenders 集合(或该集合中的所有实体)中删除用户实体时，例如通过执行这样的调用:

List<User> senders = Collections.emptyList();
user.setAssociatedSenders(senders)

数据库表已正确更新，但下一次调用 em.find(User.class, username)，其中 username 是之前访问过的用户的 ID位于 linkedSenders 集合中，表明 linkedReceivers 集合(反面)尚未正确更新。也就是说，user 仍在该集合中。仅当我通过 em.refresh() 刷新实体时，集合才会正确更新。看起来实体管理器在这里做了一些缓存，但这种行为对我来说似乎不正确。

更新也许值得一提的是，我正在 JSF 托管 bean 中的前端修改用户实体，即当实体处于分离状态时。

Answer 1

如果在分离对象时修改该对象，则必须将其 merge() 回持久性单元。由于您正在修改源对象和目标对象，因此必须 merge() 这两个对象以维护双方的关系。级联合并是不够的，因为您已经删除了对象，因此没有任何内容可以级联。

您还可以在合并之后以及提交之前和之后检查对象的状态。

也许包括您的合并代码。