Hi,
I can reduce the number down to 2. By first getting a session bean to call
on the ahome.findWherePropertyGreaterThan(int value) and retrieving the
beans (load-state=true) that have property > 7. Then the same session bean
loops through and gets the list of ids and puts them into an array and then
calls bhome.findByPrimaryKeys(int[]) with the array just created. The
Borlands Appserver 4.5 cmp engine supports the use of arrays in finders and
will construct an SQL IN clause with each array element. The problem with
this is that my direction of access will be reversed. I will move from bBean
to aBean (m->1). This movement won't result in a sql call since the list of
abeans have been previously loaded by my first find call - it will be loaded
from the entity cache.
William Louth
-----Original Message-----
From: A mailing list for Enterprise JavaBeans development
[mailto:[EMAIL PROTECTED]]On Behalf Of Avi Kivity
Sent: Thursday, May 17, 2001 6:36 PM
To: [EMAIL PROTECTED]
Subject: Re: CMP relationships in EJB2.0
> >
> > aHome.findBySomeProprety(7) ->
> >
> > select a.id, a.property
> > from a
> > where a.property > 7
> >
> > and then:
> >
> > select b.id, b.someotherfield, b.aref
> > from a, b
> > where a.id=b.aref
> > and a.property > 7
> >
> > (This would be the equivalent of a join. Alternatively, I
> > wouldn't much mind if the container requested a single SQL
> with the join)
>
> Well, it seems to me this example is way too specific to be
> handled through
> CMP. You would need to go with BMP for that. Note that you
> could actually
> use both, and leverage underlying CMR relationships to
> perform some of those
> queries for you. But for the final result, you would
> definitely need to
> write some code by hand.
I don't think this example is specific. For example, a users/groups
relationship is very similar - you want to display a table with the user
name and group name. Using finders-call-ejbload (or an equivalent), you get
the users in one shot. But then N selects are required for the groups (lets
assume a great number so caching is ineffective). The example also applies
to order line item/product name, or anywhere else a join would be used.
Possibly every nontrival table display requires a join.
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