我的情況是：帶有子消息的實體父 MainSpeech。消息又是實體附件的父級。我嘗試通過添加具有兩個新附件的新按摩來保留/合并現有的 MainSpeech。持久化/合并失敗，因為 ID_MESSAGE 為空。ID_MESSAGE 是連接 Messages with Attachment 的外鍵。//Entity MainSpeech@OneToMany(fetch=FetchType.LAZY,cascade=CascadeType.ALL,mappedBy="mainSpeech")public List<Messages> getMessages() {    return messages;}public void setMessages(List<Messages> messages) {    this.messages = messages;}//Entity Messages@ManyToOne(fetch=FetchType.LAZY)@JoinColumn(name="ID_MAINSPEECH",nullable=false)public MainSpeech getMainSpeech() {    return mainSpeech;}public void setMainSpeech(MainSpeech mainSpeech) {    this.mainSpeech = mainSpeech;}@OneToMany(fetch=FetchType.LAZY,cascade=CascadeType.ALL,mappedBy="messages")public List<Attachments> getAttachments() {    return attachments;}public void setAttachments(List<Attachments> attachments) {    this.attachments = attachments;}//Entity Attachments    @ManyToOne(fetch=FetchType.LAZY)@JoinColumn(name="ID_MESSAGE",nullable=false)public Messages getMessages() {    return messages;}public void setMessages(Messages messages) {    this.messages = messages;}