[rules-users] Re: [rules-dev] Dealing with null pointer exceptions thrown by parsing rules

David, please don't take this to be picking on you, but the rule you wrote wasn't quite correct. :) when $f : Fact() Detail(fact == $f, name == "END_SET", value == true) Detail(fact == $f, name == "SET", value = 1) Detail(fact == $f, name == "PLAYER1_SCORE", $score1 : value) Detail(fact == $f, name == "PLAYER2_SCORE', value < $score1) then ... end Match the Details to their parent Fact. I just want to make sure the newb doesn't get a combinatorial explosion and run screaming. :) And, not picking on both of you, but this should be on rules-users and not rules-dev. --- On Tue, 2/24/09, David Sinclair <dsinclair(a)chariotsolutions.com&gt; wrote: > From: David Sinclair <dsinclair(a)chariotsolutions.com&gt; > Subject: Re: [rules-dev] Dealing with null pointer exceptions thrown by parsing rules > To: "Rules Dev List" <rules-dev(a)lists.jboss.org&gt; > Date: Tuesday, February 24, 2009, 12:13 PM > Alex, please don't take this to be picking on you; this > is more a post to > everyone whom reads these forums. > > You are not writing procedural, object-oriented, or > functional code. You are > writing rules to look for patterns of objects. If > everything is done in an > eval you are losing the majority of the benefits of using a > rule engine, e.g > node sharing, indexing, etc. Flesh out your object model. > Assert all of your > objects into Working Memory. This will allow you to reason > over anything > without using evals. > > OK -- rant off -- > > Alex, you may want to try and refactor your model to be > more "rules > friendly". That way your could write rules more like > the following. > > when > $f : Fact() > Detail(name == "END_SET", value == true) > Detail(name == "SET", value = 1) > Detail(name == "PLAYER1_SCORE", $score1 : > value) > Detail(name == "PLAYER2_SCORE', value < > $score1) > > On Tue, Feb 24, 2009 at 12:39 PM, Zevenbergen, Alex < > azevenbergen(a)paddypower.com&gt; wrote: > > > Thanks for replying. > > > > > > > > rule "Player 1 wins first set " > > > > when > > > > $f : Fact() > > > > eval > ($f.getDetails().get("END_SET").toString() == > "true" && > Integer.valueOf($f.getDetails().get("SET").toString()) > > == 1 && > Integer.valueOf($f.getDetails().get("PLAYER1_SCORE").toString()) > > > > > Integer.valueOf($f.getDetails().get("PLAYER2_SCORE").toString())) > > > > then > > > > //then settle selection; > > > > end > > > > > > > > > > > > this rules runs perfectly as long as the hashmap > contained in the ‘fact’ > > object has all the required keys and their values are > not null. For the time > > being I have just changed any null values to a value > of ‘DEFAULT’ but it > > would be preferable to be able to look for > f.getDetails().get("END_SET") (for > > example) knowing that the engine that sent it might > not be in an end_set > > state so may not have added that key. > > > > > > > > That example is very basic but as I create more rules > for more sports it > > could become very cumbersome to have to ensure that > every key referenced in > > the rules is in the hashmap each time! > > > > > > > > Alex > > ------------------------------ > > > > *From:* rules-dev-bounces(a)lists.jboss.org [mailto: > > rules-dev-bounces(a)lists.jboss.org] *On Behalf Of > *David Sinclair > > *Sent:* 24 February 2009 17:27 > > *To:* Rules Dev List > > *Subject:* Re: [rules-dev] Dealing with null pointer > exceptions thrown by > > parsing rules > > > > > > > > I understand what you are saying Alex, but could you > post an example rule > > to see exactly how you are doing it? It may be that > you could simply rewrite > > the rule so you don't get the NPE. > > > > On Tue, Feb 24, 2009 at 4:24 AM, Zevenbergen, Alex > < > > azevenbergen(a)paddypower.com&gt; wrote: > > > > Hi all, > > > > > > > > I have started writing my rules packages and so have > had a decent amount of > > success. However all my rules are based on value pairs > from a hashmap object > > that is contained within my fact object. This approach > works fine if the > > parameter the rule is looking for is in the map and > has a value. > > > > > > > > But I will need to be able to pass null values to the > rules (and expect > > them to just not fire any rule that looks for that > param), however this > > always throws a null pointer exception. > > > > > > > > So my question is: Is there any mechanism to deal with > this in drools. > > > > > > > > Simply setting all nulls to a default value isn’t > preferable in this > > situation as the app is going to be used by several > different sources and > > has to be able to take in many different types of > info. > > > > > > > > Thanking you, > > > > > > > > Alex > > > > > > > ________________________________________________________________________ > > Privileged, confidential and/or copyright information > may be contained in > > this communication. 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