On 13/3/17 5:57pm, Andrus Adamchik wrote:
>
>>>>
>>>> List<Object[]> result = ObjectSelect.query(Artist.class)
>>>> .columns(Artist.ARTIST_NAME, Artist.PAINTING_ARRAY)
>>>> .select(context);
>
>
>>> For me it's not clear when do we need direct List result for toMany
>>> relationship instead of using Prefetch (or even selecting related
>>> entities explicitly).
>
> Let's ponder on this some more. In the example above there are two possible
> result mappings of to-many - each cell at index 1 can store either (1) a
> List<Painting> or (2) a Painting. Of course in the second case Artist name at
> index 0 will be repeated for each painting of a given Artist (so the result
> is flattened).
>
> In the proposed solution we throw in the first case and support the second.
> I'd like to hear opinions on the usefulness of either of the cases, and maybe
> some real life examples.
Oh, I get it now. You are suggesting in option (2) that Cayenne creates a CROSS
JOIN in sql.
Surely most of the time we are steering users to creating ObjEntities where
possible; then they have the full access to follow relations, prefetching,
pagination, etc, etc.
Sometimes you want to fetch specific columns as read-only for performance
reasons. I get that. You save on fetching data and you save time on
constructing full ObjEntities. But then why would you want to embed full
ObjEntities in the result? Any performance benefits are surely out the window.
So what's the point and the use-case?
Are users going to be confused that the ObjEntities are bound to a context and
editable/committable, but the raw columns are not?
result.get(0)[3][1].setName("The scream")
result.get(0)[2] = "Munch"
context.commit()
What is the output of this:
result = ObjectSelect.query(Artist.class)
.columns(createSelf(Artist.class))
.select(context);
Is that the same as
result = ObjectSelect.query(Artist.class)
.select(context);
would the generated SQL be the same?
Ari
--
-------------------------->
Aristedes Maniatis
GPG fingerprint CBFB 84B4 738D 4E87 5E5C 5EFA EF6A 7D2E 3E49 102A
