Greg is right if you want to keep it just using expert features.
Now if you model your Singleton as an event, you could use the timestamp
instead of create a specific attribute for that:
oldSingleton : Singleton( $id : id )
newSingleton : Singleton( id == $id, this after oldSingleton
)
Or, if you have just a few rules that use your Singleton and you activate
the STREAM mode, you could simply use a sliding window:
rule "my rule that uses the singleton"
when
$singleton : Singleton( ... ) over window:length(1)
// more patterns...
then
// do something
end
[]s
Edson
2009/8/18 Greg Barton <greg_bar...@yahoo.com>
> You need some comparable property in the singleton object that's
> monotonically increasing. Then you can have a rule like the following that
> must be of higher salience than the rules you want to protect from duplicate
> singletons. i.e.:
>
> rule "EnforceOneSingleton"
> when
> oldSingleton : Singleton( $id : id, $version : version )
> newSingleton : Singleton( id == $id, version > $version)
> then
> System.out.println( "Retracting old Singleton " +
> oldSingleton.getId() + " version " + oldSingleton.getVersion());
> retract( oldSingleton );
> end
>
> --- On Mon, 8/17/09, Justin King <justin.matthew.k...@gmail.com> wrote:
>
> > From: Justin King <justin.matthew.k...@gmail.com>
> > Subject: [rules-users] Unique events / facts in working memory
> > To: "Rules Users List" <rules-users@lists.jboss.org>
> > Date: Monday, August 17, 2009, 6:20 PM
> > I'm building an application that will
> > over time record changes in a certain component (not at any
> > set interval, could occur any time). The component can
> > possibly be uniquely identified via some kind of id. Is
> > there a way that when I insert an event / fact recording a
> > change of state in this component I can remove the previous
> > one, so as there is only ever one fact / event recording the
> > current state of the component. If the previous one existed
> > it may cause rules to fire which should not.
> >
> >
> > Cheers,
> >
> > Justin
> >
> >
> > -----Inline Attachment Follows-----
> >
> > _______________________________________________
> > rules-users mailing list
> > rules-users@lists.jboss.org
> > https://lists.jboss.org/mailman/listinfo/rules-users
> >
>
>
>
> _______________________________________________
> rules-users mailing list
> rules-users@lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/rules-users
>
--
Edson Tirelli
JBoss Drools Core Development
JBoss by Red Hat @ www.jboss.com
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