Use EJBQLQuery. It supports fetching individual columns (and does not require SQL).
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 >
