[rules-users] Chart notation, update, and infinite loops

[Greg Barton]

If you have the control fact that handles the "applied == false" condition you wouldn't need to prevent reactivation of the rule.  It would be handled by the condition.

I'm thinking Edson's accumulate suggestion would be best, at this point.

If I understand correctly, what you want is this:

1) One rule Fact/Charge activation per Charge instance, with no reactivation when the Fact is updated.
2) Other Fact dependent rule activations when the Fact is updated.

The problem with making (1) happen is that you'd still have the matched Fact being updated once per Charge, which could lead to reactivation of the rules in (2) multiple times, which you may not want.  If you use accumulate in the Fact/Charge rule, plus no-loop to prevent reactivation, you get the best of both worlds: single activation of the Fact/Charge rule, with a single update to notify other rules that the Fact has changed.

I think what you're after is some kind of "modify group," where multiple calls to modify are counted as just one, and rules are notified when the group is closed out.  I'm not sure how that would be implemented, because how do you know when the modifications are finished?  A low priority rule, possibly?  Anyway, it doesn't exist in drools, afaik.

You could do that kind of thing with an additional rule that tests for the nonexistence of an unprocessed Charge, then does the update.  Adding in the control fact for tracking Charges:

rule "Update Amount"
   when
      amountFact : Fact(name == "Amount")
      $charge : Charge()
      chargeTracker : ChargeTracker(charge == $charge, applied == false)
   then
      Double amount = amountFact.getAmount();
      Double chargeAmount = charge.getAmount();
      amountFact.setAmount(amount + chargeAmount);
      chargeTracker.setApplied(true);
      update(charge);
end

rule "Close Facts After Charges Applied"
   no-loop false
   when
      amountFact : Fact(name == "Amount")
      not ChargeTracker(applied == false)
   then
      update(amountFact);
end

You'd probablt also have to prevent the "Close Facts" rule from firing when there's just no ChargeTrackers in working memory, too. 

Give that a try.

--- On Tue, 11/4/08, Dan Seaver <dan.seaver at ge.com> wrote:

> From: Dan Seaver <dan.seaver at ge.com>
> Subject: Re: [rules-users] Chart notation, update, and infinite loops
> To: rules-users at lists.jboss.org
> Date: Tuesday, November 4, 2008, 1:55 PM
> Greg,
> 1) Yes, in this case I'm looking for the cartesian
> join.
> 2) No, I can't add a property to Charge as it's
> part of our corp Object
> Model.
> 
> However, I could create a third object that manages whether
> the Charge has
> been processed which works just fine. Unless there is a
> simpler strategy /
> technique, I'll go with that.
> 
> Do you know of any way to keep the rule from being put back
> on the agenda
> when amountFact is updated? I want other rules to know that
> it's been
> updated, just not the rule that made the change.
> 
> Dan
> 
> 
> Greg Barton wrote:
> > 
> > 1) Do you want to apply all Charges in working memory
> to all "Amount"
> > Facts?  I ask because the rule is a cartesian join
> (i.e. no relation
> > between matched objects) and that sometimes performs
> in ways users don't
> > expect. (i.e. all combinations of objects that match
> the conditions are
> > affected by the rule)
> > 2) Can you add a property to the Charge object?  Then
> you could use a
> > boolean named "applied" to prevent future
> matches.
> > 
> > Rule "Update Amount"
> >    when
> >       amountFact : Fact(name == "Amount")
> >       charge : Charge(applied == false)
> >    then
> >       Double amount = amountFact.getAmount();
> >       Double chargeAmount = charge.getAmount();
> >       amountFact.setAmount(amount + chargeAmount);
> >       update(amountFact);
> >       charge.setApplied(true);
> >       update(charge);
> > end
> > 
> > If a charge could be applied to multiple Facts you
> could maintain an
> > "appliedTo" list of Facts in the Charge, and
> check that instead of a
> > simple boolean.
> > 
> > --- On Tue, 11/4/08, Dan Seaver
> <dan.seaver at ge.com> wrote:
> > 
> >> From: Dan Seaver <dan.seaver at ge.com>
> >> Subject: [rules-users] Chart notation, update, and
> infinite loops
> >> To: rules-users at lists.jboss.org
> >> Date: Tuesday, November 4, 2008, 11:50 AM
> >> I'm trying to find a good technique for
> updating
> >> specific facts in working
> >> memory. What I'm currently doing is something
> like
> >> this:
> >> 
> >> Rule "Update Amount"
> >>    when
> >>       amountFact : Fact(name ==
> "Amount")
> >>       charge : Charge()
> >>    then
> >>       Double amount = amountFact.getAmount();
> >>       Double chargeAmount = charge.getAmount();
> >>       amountFact.setAmount(amount + chargeAmount);
> >>       update(amountFact);
> >> end
> >> 
> >> The update statement causes an infinite loop.
> >> I tried using no-loop, which works if there is 1
> charge,
> >> but not if there
> >> are more than one.
> >> 
> >> Any help with solutions or strategies would be
> much
> >> appreciated.
> >> -- 
> >> View this message in context:
> >>
> http://www.nabble.com/Chart-notation%2C-update%2C-and-infinite-loops-tp20327483p20327483.html
> >> Sent from the drools - user mailing list archive
> at
> >> Nabble.com.
> >> 
> >> _______________________________________________
> >> rules-users mailing list
> >> rules-users at lists.jboss.org
> >>
> https://lists.jboss.org/mailman/listinfo/rules-users
> > 
> > 
> >       
> > _______________________________________________
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> > 
> > 
> 
> -- 
> View this message in context:
> http://www.nabble.com/Chart-notation%2C-update%2C-and-infinite-loops-tp20327483p20329780.html
> Sent from the drools - user mailing list archive at
> Nabble.com.
> 
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