如何解决所有表的公共auto_incrementid问题

Question

我有很多表，但它们有共同的自动增量。例如，我创建了我的第一个用户，它的id为1，然后我创建了一条消息，它的id为2，然后我创建了一条对消息的注释，它的id为3，但它的id应该为1，因为我没有任何其他注释或消息

我的用户：

@Entity
@Getter
@Setter
@NoArgsConstructor

@AllArgsConstructor
@Table(name = "usr")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Column(name = "username")
    private String username;

    @Column(name = "password")
    private String password;

    @Column(name = "first_name")
    private String firstName;

    @Column(name = "last_name")
    private String lastName;

    @Column(name = "role")
    private Role role;

    @Column(name = "email")
    private String email;

    @Column(name = "status")
    private Status status;

//    @OneToMany(mappedBy = "author")
//    private List<Message> messages;

//    @OneToMany(mappedBy = "author")
//    private List<Comment> comments;

    @OneToOne
    @JoinColumn(name = "gender_id")
    private Gender gender;

    @OneToOne
    @JoinColumn(name = "address_id")
    private Address address;

    @ManyToMany
    @JoinTable(
            name = "user_subscriptions",
            joinColumns =  @JoinColumn(name = "channel_id") ,
            inverseJoinColumns =  @JoinColumn(name = "subscriber_id"))
    private Set<User> subscribers;

    @ManyToMany
    @JoinTable(
            name = "user_subscriptions",
            joinColumns =  @JoinColumn(name = "subscriber_id") ,
            inverseJoinColumns =  @JoinColumn(name = "channel_id"))
    private Set<User> subscriptions;

    @OneToOne
    @JoinColumn(name = "file_id")
    private FileEntity fileEntity;

}

我的信息：

@Getter
@Setter
@Entity
@NoArgsConstructor
@AllArgsConstructor
@Table(name = "message")
public class Message {

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

    @Column(name = "text")
    private String text;

    @Column(name = "tag")
    private String tag;

    @ManyToOne
    @JoinColumn(name = "user_id")
    private User author;

    @Column(name = "header")
    private String header;

    @Column(name = "like_count")
    private Integer likeCount = 0;

    @ManyToMany
    @JoinTable(
            name = "message_likes",
            joinColumns = { @JoinColumn(name = "message_id") },
            inverseJoinColumns = { @JoinColumn(name = "user_id")}
    )
    private Set<User> likes;

    @OneToOne
    @JoinColumn(name = "file_id")
    private FileEntity fileEntity;


}

我的评论是：

@Data
@Entity
@Table(name = "comment")
public class Comment {

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

    @Column(name = "header")
    private String header;

    @Column(name = "text")
    private String text;

    @Column(name = "like_count")
    private Integer likeCount = 0;

    @ManyToOne()
    @JoinColumn(name = "user_id")
    private User author;

    @ManyToOne()
    @JoinColumn(name = "message_id")
    private Message message;

    @ManyToMany
    @JoinTable(
            name = "comment_likes",
            joinColumns = { @JoinColumn(name = "comment_id") },
            inverseJoinColumns = { @JoinColumn(name = "user_id")}
    )
    private Set<User> likes;
}

我将感谢任何帮助。

Answer 1

hibernate的AUTO生成策略是SEQUENCE，它为所有实体创建并使用一个公共数据库序列。

要获得所需的行为，可以为每个表指定专用序列，例如，如下所述：https://stackoverflow.com/a/4561233
请注意，出于性能原因，hibernate可能会配置为一次保留多个ID，因此即使每个实体都有一个专用的序列，ID中也可能存在漏洞。

为了减少安装工作量（以及存在ID间隙的可能性），您还可以切换到IDENTITY，它在内部也为表创建并使用专用序列。然而，实体ID只有在插入时才被分配，因此可能存在性能缺陷（因为hibernate不能延迟插入，例如直到事务结束）。

https://thorben-janssen.com/jpa-generate-primary-keys/