Jpa将user_group的外键添加到实体MessageRecipient答案

【问题标题】：Jpa Add foreign key of user_group to entity MessageRecipientJpa将user_group的外键添加到实体MessageRecipient
【发布时间】：2018-09-22 18:44:39
【问题描述】：

我有四个实体 Message、User、Group、MessageRecipient。我在 Group 实体中添加了一个@ManyToMany 用户，jpa 自动创建额外的表 user_group，现在我希望这个用户组有自己的 id，所以我可以将它作为外键添加到 MessageRecipient Entity

基本上，这张图片是我试图通过 JPA 实现的

目前，我有这个

@Entity
public class Group {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    private String name;

    @ManyToMany
    private Set<User> users;

    private boolean isActive;

    private LocalDateTime dateCreated;

}

@Entity
public class Message {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    private String subject;

    @ManyToOne
    @Column(name = "creatorId")
    private User user;

    private String messageBody;

    private LocalDateTime dateCreated;

    private Integer parentMessageId;

    private LocalDateTime expiryDate;

    private Integer isReminder;

    private LocalDateTime nextRemindDate;

    private Integer remindFrequencyId;

}

@Entity
public class MessageRecipient {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @Column(name = "recipient_Id")
    private User user;


    //this is where i should have FK of the user_group table 
    private Integer recipient_group_id;

    @Column(name = "message_id")
    private Message message;

    private boolean isRead;

}

通过创建另一个实体来解决它

public class UserGroup {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;


private User user;

private Group group;

}

Group Entity 中的注解 @ManyToMany user 会发生什么情况以及由此导致的 user_group 的自动创建

【问题讨论】：

我的问题通常是 jpa 自动创建 user_group ，@K.Nicholas 那么如果我自己创建它并且仍然使用注释会发生什么，我的数据库中会有两个用户组实体吗？
@K.Nicholas 好的，我会检查一下，你能检查一下我的答案是否正确，我刚刚发布了一个解决方案
好的，我会阅读您发送的链接以了解问题，然后了解可嵌入复合键@K.Nicholas

标签： jpa

【解决方案1】：

我的解决方案是这样的实体

  @Entity
public class MessageRecipient {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @Column(name = "recipient_Id")
    private User user;

    @ManyToOne
    @Column(name = "recipient_group_id")//this is where i should have FK of the user_group table
    private UserGroup userGroup;

    @Column(name = "message_id")
    private Message message;

    private boolean isRead;
}


    @Entity
    public class Group {

        @Id
        @GeneratedValue(strategy = GenerationType.AUTO)
        private Integer id;

        private String name;

        @ManyToMany
        private Set<User> users;

        private boolean isActive;

        private LocalDateTime dateCreated;
    }

    @Entity
    public class Message {

        @Id
        @GeneratedValue(strategy = GenerationType.AUTO)
        private Integer id;

        private String subject;

        @ManyToOne
        @Column(name = "creatorId")
        private User user;
    }

【讨论】：