FAQ
Hi Ari

Not sure if this is what you are looking for, but this is what I did once:

1. Create a dbEntity in the modeler that has all the columns you are
interested in from the various tables. (So this dbEntity is more like a view
as it doesn't represent a real table.)
2. Create a read only ObjEntity in the modeler based on the 'fake'
dbEntity.
3. Create a SQLTemplate query that will retrieve the data from the various
tables.
4. Perform the query as usual (no datarows)

For example I did something like:

SQLTemplate reportTemplateQry = new SQLTemplate
(
     ReportTemplateLine.class,
     "select A.NAME, B.ORDER from RPT_GROUPS as B, PRT_TEMPLATE as A "
     +"where .... "
);

List<ReportTemplateLine> lines = ....performQuery( reportTemplateQry );


Regards
Jurgen




-----Original Message-----
From: Aristedes Maniatis
Sent: Wednesday, April 15, 2015 11:20 AM
To: user@cayenne.apache.org
Subject: lightweight object fetching

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

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