[rules-users] Getting facts from external source using 'from' and parametrized method call

[Przemysław Różycki]

Hi,

could I ask for some advice, please, how to use a parametrized method 
call to get some data using 'from' element in LHS.

To be more precise, I would like to do something like this:

rule "My Rule"
   when
     $fact : Fact(  ) from factSource.getSomeFacts("a","b","c")
   then
     // do something
end

where factSource is for example some global and 
getSomeFacts(String,String,String) is a parametrized method that returns 
some array of Fact objects.

Unfortunately, when I try to launch the following rule I have an error:

Exception in thread "main" org.mvel.PropertyAccessException: unable to 
resolve property: factSource.getSomeFacts("a","b","c")
	at 
org.mvel.optimizers.impl.refl.ReflectiveAccessorOptimizer.compileGetChain(ReflectiveAccessorOptimizer.java:295)
	at 
org.mvel.optimizers.impl.refl.ReflectiveAccessorOptimizer.optimizeAccessor(ReflectiveAccessorOptimizer.java:110)
	at 
org.mvel.ast.VariableDeepPropertyNode.getReducedValueAccelerated(VariableDeepPropertyNode.java:26)
	at 
org.mvel.ast.PropertyASTNode.initializePropertyNode(PropertyASTNode.java:70)
	at 
org.mvel.ast.PropertyASTNode.getReducedValueAccelerated(PropertyASTNode.java:24)
	at org.mvel.MVELRuntime.execute(MVELRuntime.java:90)
	at org.mvel.CompiledExpression.getValue(CompiledExpression.java:111)
	at org.mvel.MVEL.executeExpression(MVEL.java:252)
	at 
org.drools.base.dataproviders.MVELDataProvider.getResults(MVELDataProvider.java:55)
	at org.drools.reteoo.FromNode.assertTuple(FromNode.java:68)
	at 
org.drools.reteoo.SingleTupleSinkAdapter.createAndPropagateAssertTuple(SingleTupleSinkAdapter.java:55)
	at 
org.drools.reteoo.LeftInputAdapterNode.assertObject(LeftInputAdapterNode.java:116)
	at 
org.drools.reteoo.SingleObjectSinkAdapter.propagateAssertObject(SingleObjectSinkAdapter.java:22)
	at org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:162)
	at org.drools.reteoo.Rete.assertObject(Rete.java:175)
	at org.drools.reteoo.ReteooRuleBase.assertObject(ReteooRuleBase.java:192)
	at 
org.drools.reteoo.ReteooWorkingMemory$WorkingMemoryReteAssertAction.execute(ReteooWorkingMemory.java:181)
	at 
org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:1312)
	at 
org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:915)
	at 
org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:883)
	at 
org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:684)
	at com.sample.DroolsTest6.main(DroolsTest6.java:29)
Caused by: java.lang.NullPointerException
	at 
org.mvel.optimizers.impl.refl.ReflectiveAccessorOptimizer.getMethod(ReflectiveAccessorOptimizer.java:530)
	at 
org.mvel.optimizers.impl.refl.ReflectiveAccessorOptimizer.compileGetChain(ReflectiveAccessorOptimizer.java:261)
	... 21 more

Documentation says:

"The from Conditional Element allows users to specify a source for 
patterns to reason over. This allows the engine to reason over data not 
in the Working Memory. This could be a sub-field on a bound variable or 
the results of a method call."

so I assume that it is possible to do what I want. If not, could I ask 
for an advice of some workaround, please?

Best regards,
-- 
Przemysław Różycki
IT Architect
AMG.net, A Bull Group Company
ul. Łąkowa 29
90-554 Łódź
www.amg.net.pl