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

[Edson Tirelli (JIRA)]

    [ http://jira.jboss.com/jira/browse/JBRULES-1091?page=comments#action_12373405 ] 
            
Edson Tirelli commented on JBRULES-1091:
----------------------------------------

Alexander,

Yes, the problem is exactly further constraints on the null value.

I understand that in sql the result could be null, but in drools, it should only be null if the user does it on purpose, what would be wrong. Such accumulations are always initialized in the init block:

when
$c:Customer()
$totalPayments:Money()
   from accumulate( Payment ( customer == $c, $val : value )
                                   init( Money total = new Money( 0 ); )
                                   action( total.add( $val ); )
                                   reverse( total.subtract( $val ); )
                                   result( total ) )
then 
   // ...
end

Is my assumption wrong?

So, maybe we can add a null check, so that we can provide a user friendly error message, but allowing null into the engine has huge drawbacks.

On an unrelated note, did you saw the accumulate functions feature? It may be interesting for you, doing things like:

when
$c:Customer()
$totalPayments:Number()
   from accumulate( Payment ( customer == $c, $val : value )
                                   sum( $val ) )
then 
   // ...
end

You can also create your own functions in case you want to return custom objects like the Money object in your example.



> 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) 
>    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

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