[rules-users] Matching time diff

[Edson Tirelli]

    Miguel,

    You must be careful with the concept of "current date" when writing
rules in RETE: remember that RETE works in 2 stages:

1. at "insert" time, all the rule constraints are evaluated.
2. at "fire" time, the active rules are simply executed.

    Also, note that using non-time constant expressions in an inline-eval is
wrong and will give you unpredictable results. The only way to use non-time
constant expressions is at a top level eval (not inline-eval).
    So, having said all that, I suggest you use either a fact or a global to
represent your "clock", so that you have a way to control when and how the
clock is updated and use this pseudo clock to constrain your facts.

    Also, we are working on supporting temporal constructs in drools as we
speak, and as soon as we have that, we hope it will be a lot easier to write
(safe) temporal constrained rules.

    Edson


2007/10/26, Miguel Figueiredo <mfigueiredo at telbit.pt>:
>
> Hi listers,
>
> I have a fact MyFact that has a Date field in it, and I want to check if
> the
> difference between this date and the current date is greater than 10
> seconds:
>
> The function timediff() returns the difference in seconds between a date
> and
> the current date.
>
> Rule:
>
> rule myRule
>         when
>                 fact : MyFact(date : fact, eval(timediff(date) > 10));
>         then
>                 System.out.println("Greater than 10 seconds");
> end
>
> When I fire the rules, and the difference is less than 10 seconds nothing
> happens. The next time that I fire the rules and the difference is greater
> than 10 seconds nothing happens as well.
>
> How can I make this work?
>
> Best regards,
>
> Miguel
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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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