Combination of @OnRemove and ordinary cascading

Hibernate ORM
1

I can’t seem to get cascading for entity removal working. Because of the way my Data is structured, I have to use a combination of @OnRemove(action = ...) and normal cascading (e.g. @OneToOne(cascade = ...)). To better illustrate the problem, here are a few entities as an example:

@Entity
class User {
    @Id
    String username;
}

@Entity
class Post {
    @Id
    @GeneratedValue
    UUID id;

    @ManyToOne
    @OnDelete(action = OnDeleteAction.CASCADE)
    @JoinColumn(name = "user")
    User user;

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "attachment")
    Attachment attachment;
}

@Entity
class Attachment {
    @Id
    @GeneratedValue
    UUID id;

    String content;
}

As you can see, I have two unidirectional relationships, from the Post to the User and from the Post to the Attachment. I do not want to have a bidirectional relationship between either of them, because a User is included in very many Post-like entities, and an Attachment can be used by virtually anything.

You can also see the cascading I am trying to implement. It should work like this:

  1. I delete a User.
  2. All Posts of the User are deleted, specified by @OnDelete(action = OnDeleteAction.CASCADE)
  3. The Attachment of every Post is in turn deleted, specified by cascade = CascadeType.ALL in the relation Annotation.

However, this does not work as anticipated, as the user User and associated Post entities are deleted, but the Attachments are not. This is problematic, since I then have orphaned Attachments in my database, which I would have to remove manually. I have also tried specifying orphanRemoval = true, but that doesn’t do anything either.

I have a hunch on why this does not work as expected, but please correct me if I am being wrong:
As far as I know is the deletion of entities with @OnDelete handled on the database itself, specified by the foreign key constraint (something like constraint ... foreign key (user) references user (username) on delete cascade). However, the cascading using cascade = CascadeType.ALL is managed by Hibernate itself and is not done by the database.
So what I think what happens is that Hibernate tells the database to delete the User. The database then goes on deleting the User, following the foreign key constraint, also deleting the Posts. But Hibernate does not know that these Posts were deleted, so no further cascading, which would be handled by Hibernate, happens.

So, my questions are the following:
How could I make this work as expected?
Is there a way of using @OnRemove which is not done over the database?
Or the other way round, can I cascade the rest also over foreign key constraints?

I am using Spring Boot 3.1 with Hibernate 6.2.

2

How could I make this work as expected?

You’d need a database trigger that removes attachments on delete of a row, or a cleanup job/task that looks e.g. every X days for attachment rows that have no matching FK column entry.

Is there a way of using @OnRemove which is not done over the database?

No, the annotation is there to configure the foreign key constraint.

Or the other way round, can I cascade the rest also over foreign key constraints?

You could use the metamodel to find all entities which have an association to your User entity and delete these first. You can do that in a generic fashion, but I can tell you from past experience, that it is usually easier to simply mark the user as deleted with a flag and anonymize the user’s personal data e.g. by changing the name to ***** or something like that. You have to think if you really want to delete posts and attachments of something that might have use to the organization to which a user belonged to.