Hi Andrei,

I've tried to fix it but I got stuck. My fix was suggested in https://github.com/hibernate/hibernate-orm/pull/2451, the point I got stuck was described in detail in the comments on the PR I placed when I closed the PR.

To fix the issue , commit https://github.com/hibernate/hibernate-orm/commit/2bfe30009c15ea59c587d11714d4be78b14f9ad9 basically has to be reverted (and potentially HHH-9460 Closed has to be fixed in a different manner). Vlad had done so in PR https://github.com/hibernate/hibernate-orm/pull/2226 for HHH-12436 Open , but this pull request has since been stalled because Gail found some issues with respect to join generation / lazy loading. See this comment. I've asked as to what specifically causes the problem so I can have a look into it, but didn't get any response other than that the issue was already on the roadmap.

The problem is that the fix for HHH-9460 Closed caused regressions with both inserting ( HHH-12436 Open ) and fetching ( HHH-12842 Open ) OneToOne relations, making Hibernate performance totally unusable for at least my domain, since 5.2.14, 5.3.x, and 5.4.x and on. I'm just trying to get the issue on the agenda so that I do not have to go through the efforts of maintaining a custom fork of Hibernate as part of our migration to WildFly 13+ with EE8 profile.