Add information about Session/EM proxying to the Hibernate ORM documentation

[okarmazin]

Description

Pursuant to this discussion: #39231

The information about Quarkus proxying access to the single injected Session came as a surprise to me, because it is not included in the documentation at https://quarkus.io/guides/hibernate-orm

I would like to see this mentioned in the documentation since this is a surprising behavior. After all, I am injecting a single Session object into a single field, and the documentation doesn't say that accessing this field is special.

I had been injecting SessionFactory unnecessarily for the reason of needing multiple Sessions for multiple transactions. I wish I had known that accessing a single injected Session from different transactions gave me different Sessions.

Implementation ideas

No response

[quarkus-bot]

/cc @gsmet (hibernate-orm), @yrodiere (hibernate-orm)

[beikov]

FWIW, I think that the request scope enabled property kind of hints at the fact that Session/EntityManager is transaction scoped. Not sure if it needs to be mentioned more explicitly, since a transaction scope is IMO the most natural design. Wdyt @yrodiere?

[yrodiere]

I think it would be a good thing to mention in a getting started guide regardless, because not everyone is necessarily familiar with the concept of scopes and proxies, especially when starting with Quarkus or dependency injection in general. I've been there.

The problem is that we have a single guide that acts as both a getting started, tutorial and reference, so it does tend to get bloated. But I don't think adding a single line in a strategic place will worsen the situtation too much.

[beikov]

Wdyt? #49695