Has Spring-boot changed the way auto-increment of ids works through @GeneratedValue?

Question

Spring-Boot 2.0.0 seems to have modified the way Hibernate is auto configured.

Let's suppose two simple and independent JPA entities:

@Entity
class Car {
   @Id
   @GeneratedValue
   private long id;
   //....
} 

@Entity
class Airplane {
   @Id
   @GeneratedValue
   private long id;
   //....
}

Prior, using Spring-Boot 1.5.10, I was able to generate separate sequences of auto-increments, meaning that I can get a Car with 1 as primary key and an Airplane with 1 as primary key too. No correlation between them, e.g no shared sequence.

Now, with 2.0.0, when I sequentially create a very first Car then a very first Airplane, the car gets 1 as id and airplane gets 2.

It seems that he has to deal with the GeneratedType.AUTO, that is the "used by default" specified within the @GeneratedValue annotation source.
However, my reasoning seems to stop here since GeneratedType.AUTO was also set as default with the 1.5.10.

A simple workaround to fulfil my expectation is to specify the IDENTITY strategy type of generation like so:

@Entity
class Car {
   @Id
   @GeneratedValue(strategy = GenerationType.IDENTITY)
   private long id;
   //....
} 

@Entity
class Airplane {
   @Id
   @GeneratedValue(strategy = GenerationType.IDENTITY)
   private long id;
   //....
}

I can't figure out an explanation of this behavior.

What has Spring-boot 2.0.0 changed, explaining this scenario?

Answer 1

Spring Boot 2.0 uses Hibernate 5.2 (https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-2.0-Release-Notes).
Hibernate changes its GeneratedType.AUTO strategy since 5.2. Any database that does not support sequences natively (e.g. MySQL), they use the TABLE generator instead of IDENTITY. (https://hibernate.atlassian.net/browse/HHH-11014)

That's why GeneratedType.AUTO does not work as you expected.

Answer 2

You can use

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

to use MySQL autoincrement.