[jboss-jira] [JBoss JIRA] Commented: (JBRULES-1091) NullPointerException when the 'result' block of an 'accumulate' function returns null

[Alexandre Gattiker (JIRA)]

    [ http://jira.jboss.com/jira/browse/JBRULES-1091?page=comments#action_12373555 ] 
            
Alexandre Gattiker commented on JBRULES-1091:
---------------------------------------------

Thanks for the tip on accumulate functions. Indeed that is what I developed in my case, though it doesn't help on the null issue of course.

I agree with your assumption, as I understand that Drools cannot handle null facts. There is not always a direct null object available, however (such as your example with Money(0), which lacks a currency). We can still use either the Null Object pattern or a mutable object (commons-lang), something like

MutableObject(value: $totalPayments:) 
   from accumulate( Payment ( customer == $c, $val : value )
                                   init( MutableObject total = new MutableObject(); )
                                   action( total.setValue(addNullSafe( $val, total.getValue()) ); )
                                   result( total ) ) 

So the bug can only be solved in catching the error early and provide a meaningful error message.

Thank you very much for your tips. Drools is so elegant it's highly addictive :)

> NullPointerException when the 'result' block of an 'accumulate' function returns null
> -------------------------------------------------------------------------------------
>
>                 Key: JBRULES-1091
>                 URL: http://jira.jboss.com/jira/browse/JBRULES-1091
>             Project: JBoss Rules
>          Issue Type: Bug
>      Security Level: Public(Everyone can see) 
>          Components: Reteoo
>    Affects Versions:  4.0.0.GA
>            Reporter: Alexandre Gattiker
>         Assigned To: Edson Tirelli
>             Fix For: 4.0.1
>
>
> java.lang.NullPointerException
> 	at org.drools.common.DefaultFactHandle.<init>(DefaultFactHandle.java:73)
> 	at org.drools.reteoo.ReteooFactHandleFactory.newFactHandle(ReteooFactHandleFactory.java:34)
> 	at org.drools.common.AbstractFactHandleFactory.newFactHandle(AbstractFactHandleFactory.java:57)
> 	at org.drools.common.AbstractFactHandleFactory.newFactHandle(AbstractFactHandleFactory.java:48)
> 	at org.drools.reteoo.AccumulateNode.assertTuple(AccumulateNode.java:176)
> 	at org.drools.reteoo.SingleTupleSinkAdapter.createAndPropagateAssertTuple(SingleTupleSinkAdapter.java:55)
> 	at org.drools.reteoo.LeftInputAdapterNode.assertObject(LeftInputAdapterNode.java:131)
> 	at org.drools.reteoo.SingleObjectSinkAdapter.propagateAssertObject(SingleObjectSinkAdapter.java:20)
> 	at org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:168)
> 	at org.drools.reteoo.Rete.assertObject(Rete.java:168)
> 	at org.drools.reteoo.ReteooRuleBase.assertObject(ReteooRuleBase.java:190)
> 	at org.drools.reteoo.ReteooWorkingMemory$WorkingMemoryReteAssertAction.execute(ReteooWorkingMemory.java:163)
> 	at org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:1241)
> 	at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:858)
> 	at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:822)
> 	at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:623)
> 	at com.sample.DroolsTest.main(DroolsTest.java:28)
> Example rule:
> rule "Example"
> 	no-loop true
> 	when
> 		$d:		Double()
> 		from accumulate ( m : Message( $value: status ),
>                               init( double total = 0; ),
>                               action( System.out.println($value); ),
>                               result( null )
>                          )
> 	then
> 		System.out.println( "xx"); 
> 		
> end

-- 
This message is automatically generated by JIRA.
-
If you think it was sent incorrectly contact one of the administrators: http://jira.jboss.com/jira/secure/Administrators.jspa
-
For more information on JIRA, see: http://www.atlassian.com/software/jira