Use EJBQLQuery. It is old style and requires String concatenation, but supports
fetching individual columns and does not require SQL:
EJBQLQuery q =
new EJBQLQuery("SELECT p.firstName, p.lastName, sum(s.sales) FROM Person p
INNER JOIN p.sale s");
We are working to support this in ObjectSelect as well.
Andrus
> On Apr 15, 2015, at 12:20 PM, Aristedes Maniatis <a...@maniatis.org> wrote:
>
> Cayenne has very nice functionality for paging large lists of objects, so
> that the list is mostly hollow objects which are retrieved in a lazy fashion
> as they are accessed.
>
> This works well to fetch 100,000 contacts in a list and only draw the ones
> visible to the user as they scroll. What works less well is the common use
> case of a list view where you might only want to show several attributes of a
> large record.
>
> So a list of contacts might show just:
>
> * firstName
> * lastName
> * totalSales
>
> To fetch this data requires a query on contact with a prefetch to invoices.
> Lots of data being loaded from two or more tables and potentially a bit slow.
>
> Some options:
>
> 1. Use DataRows. This is simple, but you lose some of the nice
> modelling/entity features from Cayenne. You have to type all the columns
> yourself.
>
> 2. Create a view in the database with just three columns (plus a PK) and
> create a separate read-only Cayenne model which maps to that view. But now
> you are hardcoding your application to a specific database and changing the
> representation is hard.
>
> I want something half way between the two. SQLtemplate to fetch only the
> columns or aggregates I need, but mapped to some sort of read-only
> lightweight Cayenne entity.
>
>
> Has anyone tried something like this?
>
>
> Ari
>
>
>
> --
> -------------------------->
> Aristedes Maniatis
> GPG fingerprint CBFB 84B4 738D 4E87 5E5C 5EFA EF6A 7D2E 3E49 102A
>
