Collection querying support

[beikov]

The idea is to allow querying and DML for collections roles which would make a CollectionPersister the root. Syntax suggestion for referring to CollectionPersister is EntityName.collectionAttribute and also through fqn.EntityClass.collectionAttribute.
I'm pretty sure that much of the custom SQL bits in Envers could be replaced with this new feature, given that I recently saw audited collections being implemented by a specially named dynamic entity.

[gavinking]

Funnily, enough, IIRC, we used to have something quite like this in much older versions of Hibernate, and it was removed at some stage (probably because the actual implementation sucked). Re-adding something like this, but doing it properly, is something that had already occurred to me so 👍

[sebersole]

Well, yes we used to have a feature to filter a collection instance. AKA, load a Person and then filter its person.addresses by an HQL fragment. I think (though could be wrong) that that is not what Christian is talking about.

Yes, that filtering feature was removed for a number of reasons - implementation was not great, "contract" was not well defined, kludgy syntax, etc.

[erikgollot]

Hi,

I had the following discussion with Christian https://discourse.hibernate.org/t/optimize-left-join-fetch/8280/16

My usecase is as follow:
A Person has some Cats and some Dogs.
Application A issue a first select of some persons, without cats and dogs.
Then Application A sends the persons with their data to Application B to filter the list. The role of Application B is to filter the Person list using the person data plus other information known by Application B.
Application B returns a list of Person’s Ids
Application A needs to load all Dogs of the corresponding Ids

Now imagine that the loaded persons are persons whose id is : 1,2,3,…30_000
Application B returns the ids : 1, 100, 2_000, 20_000, 25_000 up to 30_000

If I use @batchsize(size=50) for example (whatever the size is)
If now I get the persons filtered by Application B and I do a person.getDogs() because I only need the Dogs of the filtrede Persons, I do not have any control on the persons for which Hibernate will load the Dogs.
Maybe, if I do a person.getDogs() for person 1, Hibernate will load persons for id = 1 up to 50. The problem is that I’m not interested by Persons 2 up to 50. The same will happen for person id=100,…and so on.
The problem with BatchSize is that the application does not have any control on the choice done by Hibernate

This is why I’ve asked for a syntax like “FROM Person p.id LEFT JOIN FETCH p.dogs” (or any other solution that allows me to retrieve only the id of a previously loaded object)…and the reason is that a Person has lot of data and returning them multiple time when I have to LEFT JOIN FETCH is not efficient.

Any comments ?