[hibernate-dev] Making APIs more Lambda-friendly

[Vlad Mihalcea]

Good idea.

So, ResultTranformer will extend both the ResultRowTransformer and
ResultListTransformer so
it will inherit both methods.

Actually, the `transformList(List list)` is only needed by
`DistinctResultTransformer`, so most of the time we'd only have to pass
`ResultRowTransformer`.

Vlad

On Tue, Mar 1, 2016 at 1:55 PM, Gunnar Morling <gunnar at hibernate.org> wrote:

> Hi,
>
> Tinkering with result transformers, I wished I'd be able to express a
> tuple transformation like this, using Java 8 Lambda-style:
>
>     session.createQuery( "SELECT foo, bar FROM Baz" )
>         .transformResultTuples( (tuple, aliases) -> { return tuple[0]
> + " " + tuple[1]; } )
>         .list();
>
> That requires an interface with a single abstract method ("functional
> interface") describing the Lambda type. The current ResultTransformer
> interface has two methods, so it cannot be used as is.
>
> I thus propose to deprecate ResultTransformer and add two new,
> separate contracts: ResultRowTransformer and ResultListTransformer.
> Query#setResultTransformer() would be superseded by two new methods:
> transformResultTuples() and transformResultList().
>
> Note that this change is fully compatible with previous Java versions:
> One still can pass an (anonymous) implementation of the contracts when
> stuck to Java 6/7. That backwards-compatible design is a really nice
> trait of how Lambdas have been added to the Java language.
>
> Lambda-friendliness is something which I think we should generally
> keep in mind when designing new APIs. Maybe there also other ones
> existing, that'd benefit from retrofitting.
>
> Any thoughts?
>
> Thanks,
>
> --Gunnar
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