[hibernate-dev] dynamic instantiation queries

[Steve Ebersole]

I'm not sure what you are getting at. This is a feature Hibernate has had
for close to 15 years.  It's not a "new feature", I'm just proposing a new
behavior to be more consistent with what people generally expect.

On Mon, Oct 24, 2016, 3:30 PM Sanne Grinovero <sanne at hibernate.org> wrote:

> Option 2# looks very nice indeed, I'd like that as it would be useful
> to be able to create immutable DTOs directly from a query; but I'm
> wondering what kind of difficulties this might pose, for example I'd
> assume the DTO constructor would be able to trigger lazy loading of
> any property of Person?
>
> Also wondering, if we expose query results as streams in the future,
> would such a feature not become obsolete?
>
>
> On 24 October 2016 at 20:38, Steve Ebersole <steve at hibernate.org> wrote:
> > So Person is your entity, e.g.:
> >
> > @Entity
> > class Person {
> >     @Id
> >     Long id;
> >     ...
> > }
> >
> > For a query like `select new DTO( p ) from Person p` Hibernate expects a
> > DTO like:
> >
> > class DTO {
> >     public DTO(Long id) {
> >         ...
> >     }
> > }
> >
> > in fact a DTO like:
> >
> > class DTO {
> >     public DTO(Person person) {
> >         ...
> >     }
> > }
> >
> > will not work with Hibernate.
> >
> > What I was proposing was for adding some support for that in 6.0 based on
> > the SQM work.  "Support" here could mean either:
> > 1) add a flag that says whether to support legacy behavior, or this new
> > behavior
> > 2) attempt to dynamically infer what to do (looks at available ctors)
> >
> > (2) would be awesome I think.  We'd still have to know how to handle
> cases
> > where the "DTO" defined ctors matching both cases and which to prefer.
> >
> >
> > On Mon, Oct 24, 2016 at 2:31 PM Vlad Mihalcea <mihalcea.vlad at gmail.com>
> > wrote:
> >
> >> Do you mean we should allow the dynamic instantiation to resolve
> entities
> >> when we pass the entity identifier?
> >>
> >> I think I saw this request on StackOverflow once.
> >>
> >> Did I understand the question properly?
> >>
> >> Vlad
> >> ------------------------------
> >> From: Steve Ebersole <steve at hibernate.org>
> >> Sent: ‎10/‎24/‎2016 22:21
> >> To: hibernate-dev <hibernate-dev at lists.jboss.org>
> >> Subject: [hibernate-dev] dynamic instantiation queries
> >>
> >> Historically (well before JPA) HIbernate would handle dynamic
> instantiation
> >> queries in cases where one of the arguments being an entity-reference by
> >> passing just the entity's identifier rather than a complete reference to
> >> the entity.  To be clear, I am talking about a query like:
> >>
> >>     select new DTO( p ) from Person p
> >>
> >> Hibernate implicitly treats this like:
> >>
> >>     select new DTO( p.id ) from Person p
> >>
> >> and expects DTO to have a ctor taking the appropriate ID type.
> >>
> >> JPA came along and also defines support for dynamic instantiation
> queries,
> >> but does not specify one way or the other how this case should be
> handled.
> >> I have been told other providers interpret this the opposite way.  Makes
> >> sense.  I think it is time we at least allow that as an option.  Or
> maybe a
> >> nicer implementation that looks for both and picks the available one (if
> >> that's not too much effort).
> >>
> >> What do y'all think?
> >> _______________________________________________
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> >>
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