The issue you're encountering stems from the fact that Hibernate (and JPA in general) doesn't fully support nested Java records, particularly when trying to map nested relationships like the Set in your RoomRecord. Hibernate is likely struggling to construct the query for the nested structure Room_.beds, which is represented as a Set.

Try and Fetch the Collection Separately, the easiest approach is to handle the Set separately. You can fetch Room and Bed entities separately, then map them manually to RoomRecord in your Java code.