I've stumbled upon a situation i cannot resolve using Hibernate documentation - i cannot alter an @ElementCollection from within the corresponding entity or even the DAO/Service.
My setup has a hibernate entity, separated into two classes:



The thing is, while excludeFromRole works, excludeFromGroup throws an exception "failed to lazily initialize a collection of role". I thought that had something to do with no open sessions, etc., but even when i explicitly call excludeFromGroup in DAO with an entityManager, it still returns the same exception.
I tried detaching the entity with EntityManager or closing the session in which it was fetched from the DB, but it didn't help.
This page https://docs.jboss.org/hibernate/orm/5. ... rmula.html says, that Formula represents a read-only state. Does this mean what i'm trying to do is effectively impossible and i have to look at @ColumnTransformer (which i can't get to work properly so far)?

Just as you concluded, @Formula gives you a read-only mapping, so you cannot benefit from the very convenient dirty checking mechanism.

What you need to do is to replace @Formula with a proper @ElementCollection mapping. For this, the groups mapping becomes:

Ok, that seems to work in @Transactional context, thank you.

I don't understand, though, what's the difference between calling remove on those 2 fields:

Even though both are lazily accessed, Roles can be changed without any opened session, and Groups - not so much.
Is there a way to make something like this work, without the need to use DAO as a proxy?

I think you're making a wrong observation. Typically, if you try to modify an entity outside of a Transaction, you get an exception.

Indeed, with all the modifications i've made to the DAO during my "investigations", i forgot that in getEntityById() i was initializing Roles with Hibernate.initialize(), which was the cause of difference in behaviour.