Re: [rules-users] Unique events / facts in working memory
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.king(a)gmail.com> wrote:
From: Justin King <justin.matthew.king(a)gmail.com>
Subject: [rules-users] Unique events / facts in working memory
To: "Rules Users List" <rules-users(a)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
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