> Oh, I get it now. You are suggesting in option (2) that Cayenne creates a
> CROSS JOIN in sql.
Actually not a CROSS join. It will be a regular INNER JOIN based on
relationship from the query root. JPA spec defines CROSS join operations. We
don't (yet?).
> 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.
Yep. A typical use case for intermixing DataObjects and scalars in the result
is this: [<artist>, <count_of_paintings>] that gives us each object's to-many
counts without resolving to-many relationships. What I am unsure though is
whether [<artist_name>, <painting>] result is of any use to anyone.
> Are users going to be confused that the ObjEntities are bound to a context
> and editable/committable, but the raw columns are not?
I am not concerned about this. I think everyone should understand that only
DataObjects can be committed. Any other representations is non-updateable data.
Andrus
> On Mar 13, 2017, at 10:29 AM, Aristedes Maniatis <a...@maniatis.org> wrote:
>
> 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
