[rules-users] How to write a rule that fires when it matches against specific facts in working memory.

[Edson Tirelli]

   Up to Drools 5, the accumulate function API supports only a single
argument to the function, but that argument can be an array or a list. So
what I do on my own implementations is to pass the $param as one element of
the array and $o as the other. It is not ideal, but it is how you can do
that in Drools 5. In Drools 6 I will change the API to support multiple
parameters, but I've been postponing that because when I do it, it will
break existing implementations of the interface.

   Anyway, if you are using the MVEL dialect, creating a list is as simple
as wrapping it in [ ], as you could see in my previous e-mail.

$options : List() from accumulate(
      $op : Option(),
      matchAll( [ ${param}, $op ] ) )

    Edson

2011/1/29 groovenarula <gnarula1 at la-z-boy.com>

>
> Edson,
>
> I did manage to use the 'CollectSetAccumulateFunction' as a template for
> the
> MatchAll and have also successfully 'called' the accumulate function from a
> rule written in a .drl file. But I'm stuck at one point - how to send the
> value of $param to the accumulate method ? From what I understand, the
> accumulate method is invoked for each fact - so if I write
>
>     MatchAll( $o ) it will invoke the accumulate method and passing $o fact
> to the method via the 'Object value' parameter.
>
> So far so go, however, I'm stuck on how to pass the value of '$param' to
> the
> accumulate method (or any other method like init, getResult for that
> matter).
>
> One option I can think of is to change the definition of the Option fact to
> include a 'param' field and then write a rule that sets the value of that
> field to $param (so every Options param field would get set to the value of
> $param). I can then extract that in the accumulate method it self. But is
> there a better way that I might be missing ?
>
> Thanks in advance,
> Gurvinder
>
> --
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> http://drools-java-rules-engine.46999.n3.nabble.com/How-to-write-a-rule-that-fires-when-it-matches-against-specific-facts-in-working-memory-tp2294599p2369936.html
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-- 
  Edson Tirelli
  JBoss Drools Core Development
  JBoss by Red Hat @ www.jboss.com
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