Re: [rules-users] Creating objects in WHEN clause

Just a comment: "There is no operator overloading in java, so the "<" operator must act on a numerical primitive. (int, double, etc.) " This is not true. Comparison operators will work on any "comparable" type. So if Quantity implements Comparable interface, it must work. Otherwise it is a bug. Although, remember that Drools always makes type coercion from the right to the left value, so, for that to actually work: Person( height < $2m ) "height" must be comparable to $2m. []s Edson 2009/2/26 Greg Barton <greg_barton(a)yahoo.com&gt; > The problem is the "Person( height < $2m )" part. There is no operator > overloading in java, so the "<" operator must act on a numerical > primitive. > (int, double, etc.) $2m is a Quantity. As for why this doesn't error > out, > I'm not sure, but it certainly won't execute. (Unless mvel has some > capabilities I'm not aware of.) > > Try > > Person( height < $2m.height ) > > ...as long as Person.height and Quantity.height are both numerical types. > > If you want to specifically call compareTo() you should use an eval > block: > > WHEN > $meter:UoM( ) from UoMs.get("length","m") > $2m:Quantity() from Quantities.get(2,$meter) > $p: Person() > eval($p.getHeight().compareTo($2m)) > > However, even if this works, I hope you're not going to be putting too > much > data through rules like this. The way it's currently constructed it > completely circumvents all of drools' indexing ability. :) The power of > rules comes from tracking the changes in a set of objects, and firing > rules > based on only the changes observed. (That set is the working memory.) > The > "from" keyword allows you to have rules that draw objects from outside > working memory, but you pay for that convenience: the cost is not being > able > to track changes. As a result, objects gathered using "from" must be > reconsidered even if they haven't changed (i.e. every time the condition > is > encountered) because drools has no way of knowing if they've changed or > not. > > So, after this long winded spiel, here's my suggestion: get the rule(s) > to > work using "from" but also try inserting the Quantity object in working > memory. If you're processing enough data with the rules you will notice > a > difference. > > --- On Thu, 2/26/09, David Boaz <davidb(a)dbmotion.com&gt; wrote: > > > From: David Boaz <davidb(a)dbmotion.com&gt; > > Subject: Re: [rules-users] Creating objects in WHEN clause > > To: rules-users(a)lists.jboss.org > > Date: Thursday, February 26, 2009, 9:13 AM > > Thanks for your all help. > > with your help, my rule looks now as: > > WHEN $meter:UoM( ) from > > UoMs.get("length","m") > > $2m:Quantity() from Quantities.get(2,$meter) > > Person( height < $2m ) > > > > My Quantity class implements Comparable interface. When > > running the rule on > > a good dataset (where I expect the rule to fire), the rule > > fails with no > > error. in addition, the compareTo(Object o) method is not > > called (the > > debugger doesn't stop in this method). > > > > Can you please help? > > Thanks, David > > > > _______________________________________________ > 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, a division of Red Hat @ www.jboss.com _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users