Hi, I've two entity types, "User" and "PhoneNumber",with two associations between them: User#phoneNumbers() and User#alternativePhoneNumbers(). By default, only one mapping table is created for these two: create table User_PhoneNumber ( Parent_id bigint not null, phoneNumbers_id bigint not null, alternativePhoneNumbers_id bigint not null ) At runtime things will fail because of the NOT NULL constraints: Only one of "phoneNumbers_id" and "alternativePhoneNumbers_id" will be set for a given association row. If I remove the constraints (e.g. pretending to work with a legacy database), things seem to work: association rows are inserted into the right columns and also are loaded correctly. My question: Should such sharing of association tables be supported or not? If yes, we'd have to adapt the generated DDL (making both columns nullable, and optionally add a check constraint to make sure exactly one is not null). For map associations, also a primary key is generated for one of the two associations, so that'd have to be adapted as well. If that's not to be supported, can we fail early on, demanding the user to specify distinct join tables? I had filed https://hibernate.atlassian.net/browse/HHH-10472 about this a while ago. But thinking about it again, I realize it actually could be made work, although it doesn't appear as a desirable mapping and I'd prefer an early error message. Any thoughts? Thanks, --Gunnar