[hibernate-dev] dynamic instantiation queries

[Steve Ebersole]

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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