This repo contains test cases demonstrating differences with association comparisons between Hibernate 5 and 6.

User and comment entities are used in the example, comment has a @ManyToOne association to a user. Adding @NotFound annotation to the association causes Hibernate to generate SQL with join instead of simple id comparison, which breaks for updates and deletes.

Example for select:

• without @NotFound - select ... from comments c1_0 where c1_0.user_id=?
• with @NotFound (both IGNORE and EXCEPTION) - select ... from comments c1_0 left join users u1_0 on u1_0.id=c1_0.user_id where u1_0.id=?

However, for updates and deletes the join is excluded and invalid SQL is produced - delete from comments where u1_0.id=?.

Without @NotFound valid SQL is generated - delete from comments where user_id=?, same SQL is generated in Hibernate 5 regardless of @NotFound presence.