@GeneratedValue(strategy = GenerationType.AUTO): MySQL 和表之间共享的生成ID？

Question

I have some tables in MySQL database. I am implementing a Spring Boot application and now testing the database. I have @Entities:

public class Author implements Serializable {
    private static final long serialVersionUID = 1L;

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

...

public class Publisher implements Serializable {
    private static final long serialVersionUID = 1L;

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

My issue is the following: When I save the above in the MySQL database, the generated IDs in the databases are "shared". By that, I mean that for example, first the Publisher table gets the ID 1, and the Author gets ID 2 and 3. Then, in the next run, Publisher gets ID 4, and Author 5 and 6. And so on. What I would like is this: That Publisher table gets IDs 1 2 3..., and Authors get IDs 1 2 3... Is this possible? I am using MySQL database and Spring Boot with JPA dependencies.

Answer 1

That happens because on any database that does not support sequences natively, such as MySQL, hibernate is using the TABLE generator instead of IDENTITY, when generation type is set to AUTO. You can check that a table with sequences of ids is generated by hibernate that will tell which id is the next one to be used (hibernate_sequence).

You are looking for the IDENTITY generator:

public class Author implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

...

public class Publisher implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

More info:

https://www.baeldung.com/hibernate-identifiers#2-identity-generation

https://hibernate.atlassian.net/browse/HHH-11014