2009/11/16 richarda <richard.ambridge@gmail.com>

I wish to have a rule that says,  if I get one event, but not another one
after a period, then do something.
But I also want to only do this once..

So, I wrote the rules: (using the eclipse sample project)



declare Message
       @role( event )
end

rule "Hello World"
       when
               $m : Message( status == Message.HELLO )
               not ( Message( status== Message.GOODBYE, this after [0s,1m] $m)) ;
       then
               System.out.println( "Hello" );
end

rule "GoodBye"
       when
               $one : Message( status == Message.HELLO )
               $two : Message( status == Message.HELLO )
       then
               System.out.println( "Two hellos, remove one" );
               retract($two);
end


But, when I run;
                       Message message = new Message();
                       message.setMessage("Hello World");
                       message.setStatus(Message.HELLO);
                       ksession.insert(message);

                       Message message2 = new Message();
                       message2.setMessage("Hello World");
                       message2.setStatus(Message.HELLO);
                       ksession.insert(message2);
                       ksession.fireAllRules();

I get:
Two hellos, remove one
java.lang.NullPointerException
       at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:970)
       at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:885)
       at org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1086)
       at
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:660)
       at
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:627)
       at
org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:183)
       at com.sample.DroolsTest.main(DroolsTest.java:38)


What am i doing wrong?
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