[rules-users] Drools 5.1 - exception when trying to use incremental KB updates.

[Stephen Mcgruer]

Just moved to Drools 5.1, using a Guvnor package as the base for a  
Knowledge Base with incremental updating enabled. Our resource is a  
Guvnor PKG. We encounter the following error when a snapshot is made:

[2010:08:224 16:08:903:debug] KnowledgeAgent: Diffing: [UrlResource  
path='http://localhost:1337/drools-guvnor/org.drools.guvnor.Guvnor/package/TEST/v0.1']
[2010:08:224 16:08:935:debug] BinaryResourceDiffProducerImpl:  
Comparing [Rule name=Resource Null-Checker, agendaGroup=MAIN,  
salience=0, no-loop=false] against [Rule name=Resource Null-Checker,  
agendaGroup=MAIN, salience=0, no-loop=false]
Exception in thread "Thread-30" org.drools.RuntimeDroolsException:  
java.lang.reflect.InvocationTargetException : [Rule name=Resource  
Null-Checker, agendaGroup=MAIN, salience=0, no-loop=false]
	at org.drools.core.util.ReflectiveVisitor.visit(ReflectiveVisitor.java:56)
	at  
org.drools.agent.impl.BinaryResourceDiffProducerImpl.diff(BinaryResourceDiffProducerImpl.java:63)
	at  
org.drools.agent.impl.KnowledgeAgentImpl.incrementalBuildResources(KnowledgeAgentImpl.java:785)
	at  
org.drools.agent.impl.KnowledgeAgentImpl.buildKnowledgeBase(KnowledgeAgentImpl.java:586)
	at  
org.drools.agent.impl.KnowledgeAgentImpl.applyChangeSet(KnowledgeAgentImpl.java:185)
	at  
org.drools.agent.impl.KnowledgeAgentImpl$ChangeSetNotificationDetector.run(KnowledgeAgentImpl.java:1106)
	at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at org.drools.core.util.ReflectiveVisitor.visit(ReflectiveVisitor.java:47)
	... 6 more
Caused by: java.lang.RuntimeException: this MVELReturnValueExpression  
must be compiled for equality
	at  
org.drools.base.mvel.MVELReturnValueExpression.equals(MVELReturnValueExpression.java:123)
	at  
org.drools.rule.ReturnValueRestriction.equals(ReturnValueRestriction.java:306)
	at  
org.drools.rule.ReturnValueConstraint.equals(ReturnValueConstraint.java:121)
	at java.util.Arrays.equals(Unknown Source)
	at org.drools.rule.OrConstraint.equals(OrConstraint.java:132)
	at java.util.AbstractList.equals(Unknown Source)
	at org.drools.rule.Pattern.equals(Pattern.java:317)
	at org.drools.rule.GroupElement.equals(GroupElement.java:273)
	at  
org.drools.agent.impl.BinaryResourceDiffProducerImpl.compareRules(BinaryResourceDiffProducerImpl.java:258)
	at  
org.drools.agent.impl.BinaryResourceDiffProducerImpl.visitRule(BinaryResourceDiffProducerImpl.java:117)
	... 11 more

The rule in question is quite straight-forward, works on the initial  
load up and worked in 5.0.1 fine. It is not the rule that was just  
changed. If I remove that rule, another is just substituted in its  
place in the error message.

What might be causing this? If you need more information, please ask.

Stephen

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