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Cascaded merge of a Many-to-many link entity generates invalid INSERT

Description

I was trying to do a Many-to-many setup with a link entity (as described in the manual).

Using the entities from the manual, when I call Session.merge after assigning an Address to a Person, Hibernate attempts to insert a (null, null) tuple into the link table. The problem only affects merge – persist seems to work fine.

I've stepped through it with a debugger and it seems, that SessionImpl.instantiate (called during the cascading merge) does not copy over the two @Id fields.

I've reproduced it with 5.2.2, 5.2.1 and 5.0.9, with both PostgreSQL and H2. Both databases won't insert the null values into the primary key, of course.

A test case is attached.

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Christian BeikovFebruary 18, 2025 at 4:41 PM

The culprit AFAICT is that both collections that refer to the link entity do specify cascading. When merging one side, the entity is replaced in that collection, whereas the other side still refers to the old/original link entity. Fixing this up manually resolves the NonUniqueObjectException, but I’m still a bit unsure if the entity needs to be copied in the first place, since we know that it doesn’t exist on the database.

Christian BeikovFebruary 18, 2025 at 4:23 PM

Spoiler alert, my idea for a fix did not work. It’s more involved.

Christian BeikovFebruary 18, 2025 at 3:22 PM

I just tested this on ORM 7 and can confirm this is still an issue. It seems to me that the issue is org.hibernate.type.ComponentType#deepCopycopies the PersonAddress component representing the id of the entity, but due to the embedded/virtual mapping, this object also acts as entity. I didn’t dig deeper, but it seems to me that returning the original value in this case is more appropriate i.e. add this override to EmbeddedComponentType:

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Created August 7, 2016 at 5:02 PM
Updated February 19, 2025 at 10:21 AM