[rules-users] Suppressing reciprocal matches

[Mark Proctor]

D Brock wrote:
> I have defined the following rule to detect when duplicate objects (in this
> example, Widgets) exist.  This always produces two matches, and therefore
> two messages.  I understand why this occurs, but I would like for only one
> message to be reported.  I cannot retract one of the widgets after a match
> b/c all are needed for additional rules matching.  Is the a conventional way
> for accomplishing the elimination of the reciprocal match?
>
> rule "Do not allow duplicate widgets"
> 	when
> 		$w : Widget( $name : name )
> 		Widget( this != $w, name == $name )
> 	then
> 		System.out.println( "Duplicate widgets found with name =  " + $name );
> end
>   
We are looking into a new conditional element that can achieve this. The 
idea is when you use this CE, it ensures only a single permutation will 
be propagated. In the meantime you can probably try something like:

$w : Widget( $name : name )
     Widget( this != $w, hashCode < $w.hashCode, name == $name )