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

[Michael B.]

Thanks for the info Edson!



Edson Tirelli-3 wrote:
> 
>    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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>>
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>>
> 
> 
> 
> -- 
> Edson Tirelli
> JBoss Drools Core Development
> Office: +55 11 3529-6000
> Mobile: +55 11 9287-5646
> JBoss, a division of Red Hat @ www.jboss.com
> 
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> 


-----
Drools Noob since 5/2008
-- 
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