[rules-users] variable instance check?

[Edson Tirelli]

   Eric,

   For now, the way to do identity checks is to use an inline eval:

when
    $a : Fact()
    $b : Fact( eval( $a == $b ) )
then
    // $a and $b are identical
end

   []s
   Edson

2007/10/18, Eric Miles <eric.miles at kronos.com>:
>
> In java, I can check to see if a 2 variables references the same
> instance as such:
>
> Object a = new Object();
> Object b = a;
>
> a == b
>
>
>
>
> Is there a way to do this in Drools?  For instance, if there is an
> object in working memory and it is a specific instance, I do not want to
> fire the rule again.  ie:
>
> rule "User Lookup UserKey"
>      salience 10000
>      when
>          com.kronos.taws.model.User(empId == null, $key:empIdKey)
>      then
>          System.out.println("Firing 2!");
>          insert($key);
>
> end
>
> I want to ensure that $key is not already in working memory.  But mind
> you, there might be other $keys that are in working memory that do not
> belong to this particular com.kronos.taws.model.User instance.  I do not
> want this rule to fire because I have subsequent rules that will make
> empId a value other than null.
>
> I attempted to do this:
>
> rule "User Lookup UserKey"
>         when
>                 com.kronos.taws.model.User(empId == null, $key:empIdKey)
>                 not UserKey(this == $key)
>         then
>                 System.out.println("Firing 2!");
>                 insert($key);
>
> end
>
> However, I still think this is doing an equality check because once the
> $key object is updated in another rule, this rule is fired again!
>
> Thanks in advance!
> Eric
>
> _______________________________________________
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> rules-users at lists.jboss.org
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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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