You have answered your question yourself: evaluation of patterns is done whenever a fact is added; salience will only order firings. Thus, the access person.name.firstName runs into the NPE. One way to cope with this would be to introduce a Name object which represents "no name", available as a public static object in Name; use this to initialize Person objects. This will still let you detect the absence of a name (name == Name.noName) but it won't run into the NPE in your second rule. -W On 6/12/09, surya_n2007 <surya_n2007(a)yahoo.co.in&gt; wrote: > > Throwing runtime exception in this example inserted person object as person > name is null. Ideally need to add error > "P01" and in second rule checks for precondition "P01" exist and skip rule. > But i am getting the below error. > Please let me know this is bug, i dont want to check again "Second Rule" > name object is not null. > I think this is happening since drools frist try to run all rules before > start execution. > > please let me know whether anything wrong on my end. > > > Rule Engine COde : > > Person person = test.new Person(); > // Name name = person.new Name(); > // person.setName(name); > workingMemory.insert(person); > > > rule "First Rule" salience 100 lock-on-active true > when > person : Person() > eval(person.name == null) > then > person.errors.add("P01"); > System.out.println("Rule 1 invoked"+person.errors); > update(person); > end > > rule "Second Rule" salience 99 lock-on-active true > when > person : Person() > eval(!person.errors.contains("P01")) > eval(person.name.firstName=="Bob") > then > person.name.suffix="Mr"; > System.out.println("Rule 2 invoked"); > end > > > > > org.drools.RuntimeDroolsException: > com.sample.Rule_Second_Rule_0Eval1Invoker@4b42aa1e : > java.lang.NullPointerException > at org.drools.rule.EvalCondition.isAllowed(EvalCondition.java:82) > at > org.drools.reteoo.EvalConditionNode.assertTuple(EvalConditionNode.java:148) > at > org.drools.reteoo.SingleTupleSinkAdapter.propagateAssertTuple(SingleTupleSinkAdapter.java:29) > at > org.drools.reteoo.EvalConditionNode.assertTuple(EvalConditionNode.java:157) > at > org.drools.reteoo.CompositeTupleSinkAdapter.createAndPropagateAssertTuple(CompositeTupleSinkAdapter.java:73) > 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.doInsert(ReteooWorkingMemory.java:71) > at > org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:911) > at > org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:883) > at > org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:684) > at com.sample.DroolsTest.main(DroolsTest.java:36) > Caused by: java.lang.NullPointerException > at com.sample.Rule_Second_Rule_0.eval1(Rule_Second_Rule_0.java:14) > at > com.sample.Rule_Second_Rule_0Eval1Invoker.evaluate(Rule_Second_Rule_0Eval1Invoker.java:20) > at org.drools.rule.EvalCondition.isAllowed(EvalCondition.java:77) > ... 14 more > -- > View this message in context: > http://www.nabble.com/Throwing-runtimeException-4.0.7-not-supposed-tp2400... > Sent from the drools - dev mailing list archive at Nabble.com. > > _______________________________________________ > rules-dev mailing list > rules-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/rules-dev > _______________________________________________ rules-dev mailing list rules-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-dev