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

[Przemysław Różycki]

Just to precise: I use Drools 4.0.7.

Best regards,
Przemek

Przemysław Różycki pisze:
> 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,