Re: Advice on using OJB collections and Struts

[Brian McCallister]

You don't need to expose the session upwards. A proxied collection in 
OJB is capable of obtaining a PersistenceBroker if the one used to 
initial obtain the instance with the collection has been closed.

The only possible hangup with this is that the work is done, typically, 
in a transaction, and if the proxy is de-referenced outside of that 
transaction there is the possibility of stale data. On the other hand, 
the the same thing holds true using hibernate with an open session and 
closed transaction, and if the data wasn't loaded into the proxy during 
the transaction, it certainly wasn't used as part of it =)

-Brian
On Dec 20, 2004, at 10:33 AM, Ray wrote:
Thanks to everyone who replied.
It seems I was thinking that it used the Hibernate
approach, which requires exposing the session right up
to the presentation layer. I imagine that OJB does the
same thing ... only the developer doesn't have to
worry about it.
Seems I have a bit more reading to do before I make a
start on the conversion, but at least it means we can
keep much of the database objects the same as they are
for Hibernte; we just have to change stuff below the
service layer that returns these objects from the
database.
Great stuff! Can't wait to get started!
Any good books on OJB, by the way?
--- Brian McCallister <[EMAIL PROTECTED]>
wrote:
I'll second this one -- the best approach I know is
just to use the
domain model object as the thing the JSP renders.
-Brian
On Dec 20, 2004, at 7:36 AM, Edson Carlos Ericksson
Richter wrote:
I've used the OJB objects and collections
directly, since they *are*
my VO.
There is no need to maintain any kind of "open
session", even if you
are using proxies (OJB will care about opening a
database session to
load object on demand)... I never used OJB + EJB,
so I can' tell you
how this could work in a distributed environment.
But with JSP accessing local datasources, I had no
problems.
Copying object to other objects/collections could
lead into unecessary
overhead.
I expect this helps.
Edson Richter
Ray escreveu:
Hi there ... :-)
I'm involved in a small project to convert from a
Hibernate backend, to OJB.
The presentation tier uses Struts and JSTL to
render
pages.
I was wondering how you OJB handles collections
attached to objects, that need to be rendered in
the
JSP pages. For example, if I have an Order object
that
contains a collection of OrderLines, and I want
to
create a page to display the whole order, then
what is
the bst way to handle this?
Is it best to copy the whole Order and OrderLines
into
some kind of VO, and then send that to the page?
Or do
you use the Hibernate approach of leaving the
session
open for the whole request cycle, so that the
JSTL on
the page, can access the collection directly from
the
Order object?
Hope that makes sense ... :-)

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--
Edson Carlos Ericksson Richter
MGR Inform�tica Ltda.
Fones: 3347-0446 / 9259-2993


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