Hibernate-使用自动FK映射集合

Question

我对ManyToSomething关系有疑问。 我无法进行注释以正确生成FK。 也许这是整个想法的错误（例如，仅通过级联保留一个实体）。

让我们在程序中的某个位置放一些简化的代码：

    Conversation conversation = new Conversation(){{
        getMessages().add(new Message());
    }};

    session.persist(conversation);

    // OR LIKE THIS:

    Message message = new Message();     
    Conversation conversation = new Conversation();

    message.setConversation(conversation);

    session.persist(message);

然后简化Hibernate批注：

@Entity
public class Message{

  @Id
  @GeneratedValue
  private int id;

  @ManyToOne
  private Conversation conversation;

}

@Entity
public class Conversation{

  @Id
  @GeneratedValue
  private int id;

  @OneToMany(mappedBy = "conversation", cascade = CascadeType.PERSIST)
  private Set<Message> messages = new HashSet<Message>();

  public Set<Message> getMessages() {
    return messages;
  }
}

因此，会话FK应该保留在消息中（一个会话-许多消息）。 但是，当Java代码运行时，数据库仅写入新的ID，而在会话端则没有FK。 这怎么可能？

更新1（仍然没有运气）：

@Entity
@Table(name = "conversation_message")
public class Message{

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(unique = true, nullable = false)
    private int id;

    @ManyToOne
    @JoinColumn(name = "conversation_id", insertable = false, updatable = false)
    private Conversation conversation;

... (other fields + getters/setters without annotation)
}

@Entity
public class Conversation{ 

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(unique = true, nullable = false)
    private int id;

    @OneToMany(mappedBy = "conversation", cascade = CascadeType.PERSIST)
    private Set<Message> messages = new HashSet<Message>();

... (other fields + getters/setters without annotation)
}

UPDATE 2（带有UPDATE 1注释），对此：

Conversation conversation = new Conversation();
conversation.getMessages().add(new Message(){{
    setConversation(conversation);
    setText("test");
}});

session.persist(conversation);

休眠日志：

insert 
        into
            conversation
            (course_id, created, name, replies, user_id) 
        values
            (null, null, null, true, null)

insert 
        into
            conversation_message
            (file, sent, text) // There is missing conversation_id at all
        values
            (null, null, "Test")

Answer 1

我在您的代码中看不到任何Id字段...您可能都缺少的是：

private Integer id;  

@Id
@GeneratedValue(strategy = IDENTITY)
@Column(name = "ID", unique = true, nullable = false)
public Integer getId() {
    return this.id;
}

然后它将在持久化时自动生成。

更新：还需要在Messages表中包含外键，您需要这样做：

@JoinColumn(name = "conversation_id", insertable = false, updatable = false)
@ManyToOne
private Conversation conversation;