[hibernate-dev] 6.0 - design question: "model navigation" exposed as an API?

[Alessio Stalla]

Well, as the developer of a framework that uses Hibernate for persistence,
I say yes to more introspection APIs :)

On 9 March 2017 at 17:35, Steve Ebersole <steve at hibernate.org> wrote:

> Currently in 6.0 we have the notion of a Navigable which models any "piece"
> of the application's domain model[1].  We also have the notion of
> a NavigableVisitationStrategy which defines the strategy for handling the
> visitation of the nodes in a Navigable tree.  In other words, Hibernate
> defines a common visitor for how to walk the application's mapped domain
> model and the NavigableVisitationStrategy implementation controls which
> sub-trees are walked; e.g. we'd use this to apply JPA EntityGraphs or to
> stop joining joinable Navigables after we have reached the
> `max_fetch_depth` setting value.
>
> It is important to note that this is very, very different from JPA's model
> and walking it.  JPA's model essentially precludes those model nodes from
> defining relational mappings as part of its type system in any sane way;
> this is due to various reasons because of the model's design[2].  This
> Navigable walking would walk the real/full relational mapping model.
>
> The design question is whether we want to expose this "domain mode walking"
> as a general public API feature.  This has been requested before; Max once
> asked for it although I forget why.
>
> Making this an API means exposing quite a few things.  Typical visitor
> pattern, the visitor (NavigableVisitationStrategy) exposes "handle" methods
> based on specific Navigable sub-types.  Those sub-types would need to be
> moved to API.  I don't have a particular concern with that, just mentioning
> it.
>
> Opinions on whether this should become an API?
>
> For sure we'd mark it @Incubating, if we decide to do it.
>
> [1] Short synopsis: Navigables include things like EntityPersister,
> CollectionPersister, EmbeddedPersister, PersistentAttribute,
> CollectionIndex, CollectionElement.  A Navigable is always relative to a
> NaviagbleSource.  NaviagbleSources are any domain Navigable
> (NavigableSource extends Navigable) which includes things like
> EntityPersister, EmbeddedPersister, SingularPersistentAttribute,
> CollectionElementEntity, CollectionElementEmbedded, etc .  The
> NaviagbleSource will be null in the case of EntityPersister (as a root),
> but in all other cases the NaviagbleSource is non-null.
>
> [2] I won't get into the reasons here, but we can certainly follow up if
> anyone challenges that assertion.
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