Re: [rules-users] Capturing condition/constraint evaluation results

There was a similar discussion going on some time ago http://drools.46999.n3.nabble.com/Anyway-to-get-Failed-Reason-for-Failed-... This said, what you are asking is not possible using the current APIs because constraints are not observable. There are ways to hack the problem, but all require a deeper understanding of the internal structure of the engine. Moreover, it would make a big difference if your use case is the general "detect whenever a constraint is not satisfied" as opposed to "find facts which can't possibly lead to ANY rule activation to be allowed to retract them". Your last message seems to point in the latter direction, is this the case? Good news is, the next version of Drools might be based on a different algorithm which will make it much easier to trace rule execution. Mark Proctor might be able to provide more details. Best Davide WARNING: Code hacks below: Just to give you an idea of the code hacks: *WARNING : not being public, these methods are subject to changes.* In the latter case, you can possibly do this: FactHandle h = ksession.insert( foo ); boolean inLeft = ((DefaultFactHandle) h).getFirstLeftTuple() != null; boolean inRight = ((DefaultFactHandle) h).getFirstRightTuple() != null; if ( ! inLeft && ! inRight ) ksession.retract( h ); if an object, after being insert, has blocked along ALL possible paths in the RETE network, it means that it won't lead to any activation (unless rules are changed) so I guess they could be safely retracted. In this case, both get methods above would return null. The more general case is much more complicated, and requires hacking either the constraints or the nodes, making them signal whenever they block an object or tuple. The code is MUCH messier, for example this is what you could do to customize the alpha nodes: RuleBaseConfiguration rbc = (RuleBaseConfiguration) KnowledgeBaseFactory.newKnowledgeBaseConfiguration(); rbc.getComponentFactory().setNodeFactoryProvider( new DefaultNodeFactory() { @Override public AlphaNode buildAlphaNode( int id, AlphaNodeFieldConstraint constraint, ObjectSource objectSource, BuildContext context ) { // Option 1: Wrap the constraint to add the behavior : // AlphaNodeFieldConstraint wrappedConstraint = new NotifyingAlphaNodeFieldConstraint( constraint ); // return super.buildAlphaNode( id, wrappedConstraint, objectSource, context ); // Option 2 : override the node behavior return new AlphaNode( id, constraint, objectSource, context ) { @Override public void assertObject( InternalFactHandle factHandle, PropagationContext context, InternalWorkingMemory workingMemory ) { final AlphaMemory memory = (AlphaMemory) workingMemory.getNodeMemory( this ); if ( getConstraint().isAllowed( factHandle, workingMemory, memory.context ) ) { this.sink.propagateAssertObject( factHandle, context, workingMemory ); } else { // Signal here System.err.println( "Constraint evaluation failed for " + factHandle ); } } }; } }); KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase( rbc ); -- View this message in context: http://drools.46999.n3.nabble.com/Capturing-condition-constraint-evaluati... Sent from the Drools: User forum mailing list archive at Nabble.com.