The above is correct, except that: this == $config1 Uses indexing and eval( $config2.equals($config1) ) Does not. So if you change your object and does not tell the engine (using modify or update), whenever the engine decides to "re-evaluate" the condition, the indexed condition will not "see" the change, while the eval() will see the change (as it is java code executing, not the engine). That is why you should always notify the engine when changing object properties. From the top of my mind, that is the only difference. Now, if you don't want duplicate objects in your session, can't you simply configure the engine to use AssertBehavior.EQUALITY instead of the default AssertBehavior.IDENTITY? KnowledgeBaseConfiguration conf = .... conf.setOption( AssertBehaviorOption.EQUALITY ); KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase( conf ); Edson 2010/11/1 H.C. <canterburry(a)gmail.com&gt;: > > We have the potential for duplicate data and so we have some rules we wrote > to de-dupe things. We are attempting the check if we have two different > objects in memory but they equal each other by equals(). We have overridden > equal() and hashCode() in all our classes. > > I came a cross two variations of the same de-duping rule that yields > different results but to me seems logically equivalent. How do these two > rules apply equality differently? > > v1: > <code>rule "Ensure no ConfigurationEntities are duplicates of others" >        when >                $config1 : ConfigurationEntity( ) >                $config2 : ConfigurationEntity( eval( $config1 != $config2 ) && this == > $config1 ) >        then >                errorList.add( new ConfigError( ConfigErrorCodes.DUPLICATE_CONFIGURATION, > $config1 )); > end</code> > > v2: > <code>rule "Ensure no ConfigurationEntities are duplicates of others" >        when >                $config1 : ConfigurationEntity( ) >                $config2 : ConfigurationEntity( ) >                eval( $config1 != $config2 && $config2.equals($config1) ) >        then >                errorList.add( new ConfigError( ConfigErrorCodes.DUPLICATE_CONFIGURATION, > $config1 )); > end</code> > > Our understanding is that: > > Given our disparate results, our assumptions must be wrong somewhere. Would > very much appreciate some insight. > -- > View this message in context: http://drools-java-rules-engine.46999.n3.nabble.com/Equality-vs-Equality-... > Sent from the Drools - User mailing list archive at Nabble.com. > _______________________________________________ > rules-users mailing list > rules-users(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/rules-users > --   Edson Tirelli   JBoss Drools Core Development   JBoss by Red Hat @ www.jboss.com