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

[Greg Barton]

Oops!  Should have "update(chargeTracker)" instead of "update(charge)" in the "Update Amount" rule below.


--- On Tue, 11/4/08, Greg Barton <greg_barton at yahoo.com> wrote:

> From: Greg Barton <greg_barton at yahoo.com>
> Subject: Re: [rules-users] Chart notation, update, and infinite loops
> To: "Rules Users List" <rules-users at lists.jboss.org>
> Date: Tuesday, November 4, 2008, 3:30 PM
> 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.
> > >> 
> > >>
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> > >> rules-users at lists.jboss.org
> > >>
> > https://lists.jboss.org/mailman/listinfo/rules-users
> > > 
> > > 
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> > >
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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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