将额外的属性添加到休眠JoinTable [英] Adding additional Property to hibernate JoinTable

问题描述

我有两个实体，消息和用户。用户与消息具有ManyToMany关系（用户可以有很多消息），消息（现在为了减少复杂性）与用户具有ManyToMany关系（消息可以发送给多个用户）。

我使用@JoinTable连接两个实体，但是，我想向连接表添加一个状态列，以确定该消息是否是新的，读取等我在考虑将该列放入Message实体中，但是，我认为这可能是不可能的。

我已经看到很多关于使用中介实体的问题的答案，但我希望尽可能避免这种情况。

有没有人有任何可能的解决方案来解决我的问题？

解决方案

JPA 2.0（即Hibernate 3.5及更高版本）引入了对建立三元关系的支持，如 Map s。例如，你可以做这样的事情（尽管如果你需要双向关系，我不知道如何处理另一方）：

  public enum MessageStatus {READ，UNREAD} 
 
 public class User {
 ... 
 
 @ElementCollection 
 @CollectionTable（name =MessagesToUsers，joinColumns = @JoinColumn（name =userId））
 @Column（name =messageStatus）
 @MapKeyJoinColumn（name =messageId）
 private Map< Message，MessageStatus> messages = new HashMap< Message，MessageStatus>（）; 
 
 ... 
} 
  

I have two entities, Message and User. User has a ManyToMany relationship to Message (A user can have many messages) and Message (for now, to make it less complex) has a ManyToMany relationship to User (a message can be sent to multiple users).

I am joining the two entities using @JoinTable, however, I would like to add a "status" column to the join table to tell if the message is new, read, etc. I was thinking of putting the column in the Message entity, however, I'm thinking this is probably not possible.

I've seen a lot of answers to this question saying to use an intermediary entity, but I would like to avoid that if possible.

Does anyone have any possible solution to my problem?

解决方案

JPA 2.0 (i.e. Hibernate 3.5 and above) introduced a support for modeling ternary relationships as Maps. For example, you can do something like this (though I'm not sure what to do with the other side if you need a bidirectional relationship):

public enum MessageStatus { READ, UNREAD }

public class User {
    ...

    @ElementCollection
    @CollectionTable(name = "MessagesToUsers", joinColumns = @JoinColumn(name = "userId"))
    @Column(name = "messageStatus")
    @MapKeyJoinColumn(name = "messageId")
    private Map<Message, MessageStatus> messages = new HashMap<Message, MessageStatus>();

    ...
}

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