[rules-users] DAO call in LHS

[Greg Barton]

'from' returns one element from the collection you target, not all of them.  If you wish to continue that approach you should use collect of accumulate.

Is the dao object in working memory?  If so, just match it and test for the list size there:

when 
  Dao(list.size > 0)
then 
  System.out.println("DAO call is successful!");
end

Of course, your current implementation of Dao.getList(), since it returns Collections.EMPTY_LIST, will not match this rule anyway. 

--- On Fri, 11/28/08, techy <techluver007 at gmail.com> wrote:

> From: techy <techluver007 at gmail.com>
> Subject: Re: [rules-users] DAO call in LHS
> To: rules-users at lists.jboss.org
> Date: Friday, November 28, 2008, 4:52 PM
> I tried following simple rule with dao call and still no
> luck. getting
> "org.mvel.PropertyAccessException: unable to resolve
> property:
> dao.getList()".  could not figure out what is wrong.
> some help please.
> 
> rule "Test DAo call"
> when 
> 	count : List(size > 0) from dao.getList()
> then 
> 	System.out.println("DAO call is successful!");
> end
> 
> dao.getList() definition:
> 
> 
>  public List<Integer> getList(){
>         return Collections.EMPTY_LIST;
>     }
> 
> Exception stackTRace:
> 
> org.mvel.PropertyAccessException: unable to resolve
> property: dao.getList()
> 	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$WorkingMemoryReteAssertAction.execute(ReteooWorkingMemory.java:181)
> 	at
> org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:1312)
> 	at
> org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:915)
> 	at
> org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:883)
> 	at
> org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:684)
> 	at
> org.drools.reteoo.ReteooStatelessSession.execute(ReteooStatelessSession.java:160)
> 	at DAOCallTest.main()
> Caused by: java.lang.NullPointerException
> 	at
> org.mvel.optimizers.impl.refl.ReflectiveAccessorOptimizer.getMethod(ReflectiveAccessorOptimizer.java:530)
> 	at
> org.mvel.optimizers.impl.refl.ReflectiveAccessorOptimizer.compileGetChain(ReflectiveAccessorOptimizer.java:261)
> 	... 22 more
> 
> 
> Michal Bali-2 wrote:
> > 
> > this blog post may be of use
> >
> http://blog.athico.com/2007/06/chained-from-accumulate-collect.html
> > 
> > 
> > On Wed, Nov 26, 2008 at 9:08 PM, techy
> <techluver007 at gmail.com> wrote:
> > 
> >>
> >> though I referred other thread about this topic,
> I'm not successful to
> >> make
> >> a
> >> dao call.
> >> I beg your pardon to ask again.
> >>
> >> 1. I want to pass the fact object to the dao
> function which returns
> >> boolean.
> >> I tried following rule and getting "
> >> Unexpected token '$fact'" as eclipse
> compilation error. Please guide with
> >> right syntax.
> >> global RuleDAO dao;
> >>
> >> rule "test DAO call"
> >>  $fact : Fact(some condition)
> >>  fact : Fact(dao.isValid($fact))
> >> then
> >> #do something
> >> end
> >>
> >> 2. Will be there any performance issue for above
> kind of rule?
> >>
> >> Thanks
> >>
> >> --
> >> View this message in context:
> >>
> http://www.nabble.com/DAO-call-in-LHS-tp20709043p20709043.html
> >> Sent from the drools - user mailing list archive
> at Nabble.com.
> >>
> >> _______________________________________________
> >> rules-users mailing list
> >> rules-users at lists.jboss.org
> >>
> https://lists.jboss.org/mailman/listinfo/rules-users
> >>
> > 
> > _______________________________________________
> > rules-users mailing list
> > rules-users at lists.jboss.org
> > https://lists.jboss.org/mailman/listinfo/rules-users
> > 
> > 
> 
> -- 
> View this message in context:
> http://www.nabble.com/DAO-call-in-LHS-tp20709043p20741585.html
> Sent from the drools - user mailing list archive at
> Nabble.com.
> 
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