Re: [rules-users] Date arithmetic in “when†session

[Edson Tirelli]

   Michael,

   Just an important note, that sometimes is overlooked by users:

*** Inline evals and return value predicates MUST be time constant ***

   It means that an inline eval() must return the exact same value if it is
executed now, or in 5 minutes from now, or whatever. So, it is not advisable
for you to write the constraint as you did.
   The correct way would be to use a top level eval() that does not suffer
from the same restriction:

  MyFact( $value : value )
  eval( $value.before(DateHelper.getModifiedDate(-6, "MONTHS")))

    The use of a non-time-constant inline eval (or return value predicates)
causes unpredictable behavior in the engine.

    []s
    Edson


2008/5/7 Michael B. <michael.bain at mckesson.com>:

>
> I dont know if this is still outstanding since the original post seems to
> have disappeared, but this is what I did during my proof of concept that I
> am going through:
>
> In a helper class (i.e. DateHelper) I had this method:
>
>    public static Date getModifiedDate(int amount, String unit) {
>        Calendar cal = Calendar.getInstance();
>        cal.setTime(getNow());
>        BusinessObject.stripTime(cal);
>
>        int calUnit = Calendar.DAY_OF_YEAR;
>
>        if (UNIT_MONTHS.equals(unit))
>            calUnit = Calendar.MONTH;
>        else if (UNIT_YEARS.equals(unit))
>            calUnit = Calendar.YEAR;
>
>        cal.add(calUnit, amount);
>        return cal.getTime();
>    }
>
> Then in my rule it would be like this:
>
>  MyFact( eval( value.before(DateHelper.getModifiedDate(-6, "MONTHS"))))
>
> Hope that helps.
>
> -----
> Drools Noob since 5/2008
> --
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> Sent from the drools - user mailing list archive at Nabble.com.
>
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-- 
Edson Tirelli
JBoss Drools Core Development
Office: +55 11 3529-6000
Mobile: +55 11 9287-5646
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