Spring Data JPA - @GeneratedValue annotation shows no affect

Question

I have a problem regarding my implementation of a weak entity type. (Note, if that's important: I'm using H2 as my database)

Here is my datamodel:

I'm trying to implement Activity's concatenated primary key using two @ID annotated columns. Here is my activity class as well as its "owner"-class:

@Entity
public class Activity {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Id
    @ManyToOne
    @JoinColumn
    private UserGroup group;

    ...
}

@Entity
public class UserGroup {

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

    ...
}

My expected outcome would be, that inside my activity table id is generated by default as identity and group_id is set depending on the corresponding group-join. Basically something like this:

create table activity
(
    id              bigint generated by default as identity,
    begin_date_time timestamp(6),
    end_date_time   timestamp(6),
    name            varchar(255) not null,
    note            varchar(255),
    group_id        bigint not null,
    room_id         bigint,
    primary key (group_id, id)
);

Instead, spring disregards my @GeneratedValue annotation and sets it to group_id, ignoring my actual activity.id column:

create table activity
(
    id              bigint       not null,
    begin_date_time timestamp(6),
    end_date_time   timestamp(6),
    name            varchar(255) not null,
    note            varchar(255),
    group_id        bigint generated by default as identity,
    room_id         bigint,
    primary key (group_id, id)
);

This is a problem, as I plan on using Rest-Endpoints and Repositories to run CRUD operations using HTTP-requests. Having an ID-counter that increments and gets new IDs for one table only seems unnecessary and dirty.

Can somebody explain to me why this is happening? Can I manually annotate group_id as a manually assigned field as a quick workaround?

Cheers!

Answer 1

What you are looking for is a composite key, which you can create with either @IdClass or with @Embeddable and @EmbeddedId . The catch is, however, that neither of these approaches will work with a @GeneratedId.

If you think about it, there's no need to have a composite key where one of the parts is autogenerated. Just have one Id on your entity that's auto generated, and if you want, create an index across (group_id, id) .