Re: Records and result auto-mapping

We already have map(Function) method available in both ColumnSelect
and SQLSelect that allows to map result from Object[] to anything via
provided function.
Here is an example from tests [1]:

List<ArtistDataWrapper> result = SQLSelect.columnQuery("SELECT * FROM
ARTIST_CT",
      Integer.class, String.class, LocalDateTime.class)
      .map(ArtistDataWrapper::new)
      .select(context);

And I experimented with simple PojoMapper that does almost exactly
what you are suggesting. Not sure if it's available though.

[1] https://github.com/apache/cayenne/blob/336f0e5297fe6ccdc3b1904ab4f6ee2c6d1ab9dc/cayenne-server/src/test/java/org/apache/cayenne/query/SQLSelectIT.java#L273

On Thu, Jul 14, 2022 at 10:52 PM Andrus Adamchik <[email protected]> wrote:
>
> Java 17 "records" create some interesting possibilities as quick DTOs. Mapping complex SQL is still rather painful in Cayenne. You'd get an Object[] as a result and/or need complex scripting within SQL. I think records and some API tweaks can help:
>
> 1. SQL result mapping.
>
> record MyRecord(String lastName, String firstName) {} // non-persistent, not in DataMap
>
> SQLSelect.query("select * from x")
>
>   // new API analogous to "#result" directive but simpler to use
>   // also we can implement some implicit name conversions ("AB_C" -> "abC")
>   .resultColumn(0, "firstName")
>   .resultColumn("LAST_NAME", "lastName")
>
>   // new API - auto-mapping the result to a POJO (record in this case)
>   .selectAs(MyRecord.class, context);
>
>
> 2. Entity result mapping (e.g. a replacement of column and data row queries).
>
> class MyEntity extends _MyEntity {} // Persistent
> record MyEntityDTO(..) {}  // non-persistent, not in DataMap
>
> List<MyEntityDTO> result = ObjectSelect(MyEntity.class)
>   .where(MyEntity.NAME.like("Joe"))
>   .prefetch(MyEntity.ANOTHER.joint())
>
>   // new API - auto-mapping the result to a POJO (record in this case)
>   .selectAs(MyEntityDTO.class, context);
>
> It will be faster than fetching MyEntity (without ObjectContext registration, uniquing, merging), and will be a good replacement of column queries API, requiring no explicit column declarations, and producing a specific type instead of Object[]. Prefetches can be auto-mapped to record hierarchies.
>
> Both examples would work with either records or regular POJOs, it is just that record definitions are so easy to create on the spot, that they can be used in a multitude of very narrow contexts.
>
> Andrus
>


-- 
Best regards,
Nikita Timofeev