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

[Dan Seaver]

Earnie,
I could certainly qualify which charges I want to use to increment the total
in amountFact. The example is illustratrating the problem with using the
technique of assigning a variable name, via chart notation, to an object in
Working Memory so that you can update the object in the consequences section
(then clause) of the rule.

Because amountFact is updated, it puts the rule back on the agenda to be
processed again, even though  the properties that are being used by the rule
qualification (when clause) have not changed.

So, if I remove the update statement, the rule behaves properly and
amountFact contains a total of all of the amounts in the charges that have
been inserted into Working Memory.

However, if I have another rule that looks at the amountFact's amount, it
won't see the updates to the property and won't fire. For example:

rule "Test Amount"
   when
      Fact(name == "Amount", amount > 150)
   then
      System.out.println("Amount is greater than 150");
end



Earnie D wrote:
> 
> Dan,
> 
> Why would you have more than one Charge when you are not qualifying it?
> Are they all the same? Do you not care which one matches?
> 
> Earnie!
> 
> 
> 
> ________________________________
> From: Dan Seaver <dan.seaver at ge.com>
> To: rules-users at lists.jboss.org
> Sent: Tuesday, November 4, 2008 12:50:09 PM
> Subject: [rules-users] Chart notation, update, and infinite loops
> 
> 
> 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.
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