The following code works, but I think it's ugly. the classes are: DescribedAddress is a base class for addresses VendorAddress extends DescribedAddress and implements method abcScore() Step getLocations() is defined as a list of DescribedAddress objects but it can also contain VendorAddress objects since they are a kind of DescribedAddress the LHS of the rule below extracts the VendorAddress with the highest abcScore from step.locations if I omit the eval(), i get ClassCastException on any DescribedAddress in locations, since DescribedAddress cannot be cast to VendorAddress. is there a more elegant / clean / efficient way to get only the VendorAddress objects from locations? rule "Find highest scored address" dialect "mvel" when $step : Step() $location : VendorAddress (eval($location instanceof VendorAddress ), abcScore>9) from $step.getLocations() not $addr : VendorAddress (eval($addr instanceof VendorAddress ),abcScore > $location.abcScore) from $step.getLocations() then System.out.println("high score is: " + $location.getAbcScore()); end -- View this message in context: http://drools.46999.n3.nabble.com/Getting-one-type-from-a-collection-of-m... Sent from the Drools: User forum mailing list archive at Nabble.com. _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users

Thank you for the hints. I have implemented a method to hide the instanceof code, and tried using the accumulate CE. The LHS of my rule is now: $step : Step() $highScore : Number() from accumulate ( $location : VendorAddress () from $step.job.scorableLocations, max($location.abcScore) ) in my RHS I can display the score this way: System.out.println(" MAX SCORE IS: " + $highScore ); and verify that the accumulate is indeed choosing the max score. HOWEVER, what I really want is not the max score, but the ADDRESS with the max score. if I try to use $location in my RHS like this: System.out.println("high score is: " + $location.getAbcScore()); I get compile time exception: [Error: unable to resolve method using strict-mode: org.drools.spi.KnowledgeHelper.$location()] It looks like my $location variable is usable in the LHS but does not get scope to the RHS. -- View this message in context: http://drools.46999.n3.nabble.com/Getting-one-type-from-a-collection-of-m... Sent from the Drools: User forum mailing list archive at Nabble.com. _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users