Peter Fuerholz ( https://hibernate.atlassian.net/secure/ViewProfile.jspa?accountId=5e468be... ) *commented* on HHH-13866 ( https://hibernate.atlassian.net/browse/HHH-13866?atlOrigin=eyJpIjoiYTkwM2... ) Re: OneToOne-association produces error on 5.4.0+ when using PostgreSQL ( https://hibernate.atlassian.net/browse/HHH-13866?atlOrigin=eyJpIjoiYTkwM2... ) Thanks for trying to help me. I do save PaymentDO before PaymentBatchJob. (see my comment above “What I want to do is saving a PaymentDO and then add a PaymentBatchJobDO to it (using Spring's JpaRepository). Strangely when trying to save the PaymentBatchJobDO this fails.“) The code worked with hibernate-core 5.3.* but no longer with hibernate-core 5.4.*. As you can see Spring is calling EntityManager.merge which leads to this issue. As a workaround I managed now that in that case EntityManager.save gets called. ( https://hibernate.atlassian.net/browse/HHH-13866#add-comment?atlOrigin=ey... ) Add Comment ( https://hibernate.atlassian.net/browse/HHH-13866#add-comment?atlOrigin=ey... ) Get Jira notifications on your phone! Download the Jira Cloud app for Android ( https://play.google.com/store/apps/details?id=com.atlassian.android.jira.... ) or iOS ( https://itunes.apple.com/app/apple-store/id1006972087?pt=696495&ct=Em... ) This message was sent by Atlassian Jira (v1001.0.0-SNAPSHOT#100126- sha1:9bc00fe )