[rules-users] Sliding windows and event retraction

[Wolfgang Laun]

On 23 March 2011 21:11, jwillans2 <james.willans at ceteva.com> wrote:

> Any help with the query below would be much appreciated.  I am assuming
> that
> event retraction is not automatic using the pattern below, however I am
> trying to come by an approach to ensuring only one event exists on an entry
> point at any moment in time.  One thought was that when a rule inserts a
> new
> event, it first retracts the previous event, although I think that a rule
> cannot have state and can therefore not maintain a handle to the previously
> inserted event?


But a fact can have state. Event() is the event.

declare Window
  event: Event
end

rule createWindow
when
  $e:  Event()
  not Window()
then
  insert( new Window( $e ) );
end

rule pushWindow
when
    $e:  Event()
    $w: Window()
then
   retract( kcontext.getKnowledgeRuntime().getFactHandle( $e.getEvent() ) );
   modify( $w ){ setWindow( $e ) );
end

-W





>  What would be a good approach to achieving this?
>
> Many thanks,
>
> James
>
>
> jwillans2 wrote:
> >
> > Hello,
> >
> > I am using sliding windows in the form:
> >
> > Obj(..) over window:length(1) from entry-point EP1
> >
> > Where many events are being inserted into EP1.  Reading the documentation
> > I expected Drools to infer from the window length that all events on EP1
> > apart from the latest one can be retracted, is this correct?  The reason
> I
> > ask is that I am not seeing retraction of events from EP1 when I debug
> the
> > session, and I am see behaviour which suggests the rule is firing against
> > old events on the entry point.
> >
> > Basically I want to get to simulate that an entry point can only contain
> > one event at any point in time and that this event is the latest one to
> > arrive.
> >
> > Thanks,
> >
> > James
> >
>
>
> --
> View this message in context:
> http://drools-java-rules-engine.46999.n3.nabble.com/Sliding-windows-and-event-retraction-tp2711810p2722062.html
> Sent from the Drools - User mailing list archive at Nabble.com.
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