[rules-users] Checking for a lack of an object

[Chris Richmond]

Well..I insert some objects, fire the rules and this rule will trigger 
the first time (when it finds no object with those characterstis) but 
every time after than when I insert more objects and fire the rules, the 
rule never fires again. I have no idea why.  Here is my simple test case.

Two clasess: TestMain and TestObject and rule file Test.drl I have 
included below.

It insterts a group of facts at one time, fires the rules, and retracts 
all those facts from the stream.  I have an event listener on the 
session, as you see to verify injections and retractions are occuring.
So the rule fires on the first batch, but on no other batches after 
that???? What gives????

Among the Inserttion and retraction events I only see:

A proper object does not exist

One time, during firing rules on the first batch.  Why does this rule 
never fire again, even though every single batch of objects I 
insert/retract does not contain the proper rule values, and so should 
fire the rule.

What is going on???





TestMain.java *************************************

package com.sample;

import java.util.ArrayList;
import java.util.List;

import org.drools.KnowledgeBase;
import org.drools.KnowledgeBaseConfiguration;
import org.drools.KnowledgeBaseFactory;
import org.drools.builder.KnowledgeBuilder;
import org.drools.builder.KnowledgeBuilderError;
import org.drools.builder.KnowledgeBuilderErrors;
import org.drools.builder.KnowledgeBuilderFactory;
import org.drools.builder.ResourceType;
import org.drools.conf.EventProcessingOption;
import org.drools.event.rule.ObjectInsertedEvent;
import org.drools.event.rule.ObjectRetractedEvent;
import org.drools.event.rule.ObjectUpdatedEvent;
import org.drools.event.rule.WorkingMemoryEventListener;
import org.drools.io.ResourceFactory;
import org.drools.runtime.KnowledgeSessionConfiguration;
import org.drools.runtime.StatefulKnowledgeSession;
import org.drools.runtime.conf.ClockTypeOption;
import org.drools.runtime.rule.FactHandle;
import org.drools.runtime.rule.WorkingMemoryEntryPoint;

public class TestMain {

   @SuppressWarnings("restriction")
   public static void main(String[] args) {


     try {

       KnowledgeSessionConfiguration config = 
KnowledgeBaseFactory.newKnowledgeSessionConfiguration();
       config.setOption( ClockTypeOption.get("realtime") );


       KnowledgeBase kbase;
       kbase = readKnowledgeBase();
       final StatefulKnowledgeSession ksession = 
kbase.newStatefulKnowledgeSession();

       WorkingMemoryEntryPoint myStream = 
ksession.getWorkingMemoryEntryPoint("My Stream");

       ksession.addEventListener(new WorkingMemoryEventListener(){

         @Override
         public void objectInserted(ObjectInsertedEvent oie) {
           System.err.println("Inserted: " + oie.toString());

         }

         @Override
         public void objectRetracted(ObjectRetractedEvent arg0) {
           System.err.println("Retracted: " + arg0.toString());

         }

         @Override
         public void objectUpdated(ObjectUpdatedEvent arg0) {
           // TODO Auto-generated method stub

         }

       });


       for (int a = 0; a < 1000; a++){
         List<FactHandle> factHandles = new ArrayList<FactHandle>();
         for (int x = 0; x < 6; x++){

           double reading = 11.3;
           float f = (float)reading;
           TestObject dr = new TestObject("Reading " + x, f);
           FactHandle fh = myStream.insert(dr);
           factHandles.add(fh);



         }
         ksession.fireAllRules();
         for(FactHandle fh : factHandles){
           myStream.retract(fh);
         }
         Thread.sleep(4000);
       }

     } catch (Exception e) {
       // TODO Auto-generated catch block
       e.printStackTrace();
     }

   }

   @SuppressWarnings("restriction")
   private static KnowledgeBase readKnowledgeBase() throws Exception {
     KnowledgeBuilder kbuilder = 
KnowledgeBuilderFactory.newKnowledgeBuilder();
     kbuilder.add(ResourceFactory.newClassPathResource("Test.drl"), 
ResourceType.DRL);
     KnowledgeBuilderErrors errors = kbuilder.getErrors();
     if (errors.size() > 0) {
       for (KnowledgeBuilderError error: errors) {
         System.err.println(error);
       }
       throw new IllegalArgumentException("Could not parse knowledge.");
     }

     KnowledgeBaseConfiguration kbConfig = 
KnowledgeBaseFactory.newKnowledgeBaseConfiguration();
     kbConfig.setOption( EventProcessingOption.STREAM );
     KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase(kbConfig);
     kbase.addKnowledgePackages(kbuilder.getKnowledgePackages());




     return kbase;
   }




}

TestObject.java *************************************
package com.sample;

public class TestObject {



   private String name;
   private float reading;


   public TestObject(String name, float reading){
     this.name = name;
     this.reading = reading;
   }


   public String getName() {
     return name;
   }


   public void setName(String name) {
     this.name = name;
   }


   public float getReading() {
     return reading;
   }


   public void setReading(float reading) {
     this.reading = reading;
   }
}


Test.drl*************************************************
#created on: Aug 19, 2011
package com.sample



rule "Test For Lack of Objects with criteria"

when
         not(TestObject(name=="blah")  from entry-point "My Stream")
then
         System.err.println("A proper object does not exist");
end




On 8/18/2011 8:46 PM, Wolfgang Laun wrote:
> On 19 August 2011 15:17, Chris Richmond <crichmond at referentia.com 
> <mailto:crichmond at referentia.com>> wrote:
>
>     How do I fire a rule if an object with certain characterstics does not
>     exists.
>
>     For example my class Foo, if I have a rule:
>
>     rule "Identify Foos with values"
>
>     when
>             Foo(stringProp=="blah", intProp==5)
>     then
>             System.err.println("A Foo was found!");
>     end
>
>
>     So how do I check for lack of existence of an object with certain
>     characteristics
>
>     I tried:
>     rule "Flag missing Foos with values"
>
>     when
>             not(Foo(stringProp=="blah", intProp==5))
>     then
>             System.err.println("A proper foo does not exist");
>     end
>
>
> That's the way to do it.
>
>
>     I also tried:
>     rule "Flag missing Foos with values"
>
>     when
>             not(exists(Foo(stringProp=="blah", intProp==5)))
>     then
>             System.err.println("A proper foo does not exist");
>     end
>
>
> Since not( Foo(...)) means "if no Foo(...) exists", the addition of 
> "exists" is superfluous and generally considered bad style (even 
> though some systems accept it to mean just "not".
>
> -W
>
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>
>
>
>
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