[rules-users] Suppressing reciprocal matches

[Swindells, Thomas]

There is a bug here though if the hashcodes are equals.

You need to make it 
 $w : Widget( $name : name )
     Widget( this != $w, hashCode <= $w.hashCode, name == $name )

And live with the fact there is a chance that the rule does fire twice - which is probably a better scenario that it failing to fire at all.  Be particularly careful if your widget overrides the equals() method as it should also override the hashcode operator to make it the case that if a.equals(b) then a.hashcode()==b.hashcode().

Thomas
> -----Original Message-----
> From: rules-users-bounces at lists.jboss.org [mailto:rules-users-
> bounces at lists.jboss.org] On Behalf Of D Brock
> Sent: 07 November 2009 16:04
> To: rules-users at lists.jboss.org
> Subject: Re: [rules-users] Suppressing reciprocal matches
> 
> 
> Thanks Mark, sounds good.  And the hashCode trick works.  Wow, I would
> have
> never thought of that!
> 
> 
> Mark Proctor wrote:
> >
> > 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 )
> >
> >
> >
> >
> > _______________________________________________
> > rules-users mailing list
> > rules-users at lists.jboss.org
> > https://lists.jboss.org/mailman/listinfo/rules-users
> >
> >
> 
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> reciprocal-matches-tp26230834p26241896.html
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> 
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