[rules-users] on update

[Edson Tirelli]

   Sergey,

   I don't think you will get the behavior you described, out of the box.
What you can do, is delegate to the engine the actual update work.

rule "on updated cost write to archive old value"
        when
                $cost : Cost( $oldAmount : amount )
                $event : CostUpdateEvent( $newAmount : amount, object ==
$cost )
        then
                //... write to archive $oldAmount
                $cost.setAmount( $newAmount );
                update( $cost );
                retract( $event );
end

   Right now, shadow facts don't expose it's cache for use in rules in a
safe way. So, I believe something like the above is the best approach.

    []s
    Edson

2007/8/2, Manukyan, Sergey <SManukyan at lear.com>:
>
>
> Folks,
>
> I need a rule that will track changes to cost amount and do something
> with his old value.
>
> Like that :
>
> rule "on updated cost write to archive old value"
>         when
>                 cost : Cost()
>                 old_cost : Cost(amount != cost.amount)  // how can I
> specify the OLD cost object before it was updated???
>         then
>                 ... write to archive $old_cost.amount
> end
>
>
> Is it possible at all?
>
> Something like in database system triggers, when you have "on update"
> and then you have OLD value and NEW values available...?
>
> Thanks a lot!
>
> -Sergey
>
>
>
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-- 
  Edson Tirelli
  Software Engineer - JBoss Rules Core Developer
  Office: +55 11 3529-6000
  Mobile: +55 11 9287-5646
  JBoss, a division of Red Hat @ www.jboss.com
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