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

From: Edson Tirelli <tirelli(a)post.com&gt; Subject: Re: [rules-users] Creating objects in WHEN clause To: greg_barton(a)yahoo.com Date: Sunday, March 1, 2009, 6:19 PM Hold on. :) We are talking about Drools, not java. When you write a pattern: SomeClass( foo < $otherFoo ) Drools will use its own implementation of "<" to make the comparison. It does not delegate that to java and so it must work. If does not work, it may be a bug, but our tests work for that: http://anonsvn.jboss.org/repos/labs/labs/jbossrules/trunk/drools-core/src... Take a look at testObject(). []s Edson 2009/3/1 Greg Barton <greg_barton(a)yahoo.com&gt; > Oh, you dun thrown down the gauntlet now. :) > > The following will not compile with java6: > > public class ComparableFu { > > static class Foo implements Comparable<Foo> { > > private int foo; > > public Foo(int foo) { > this.foo = foo; > } > > public int compareTo(Foo other) { > if(other.foo < foo) { > return -1; > } else if(other.foo == foo) { > return 0; > } else { > return 1; > } > } > } > > public static void main(String[] args) { > System.out.println(new Foo(1) < new Foo(2)); //Baaaaad! > } > } > > Methinks the overloading of comparison operators for Comparables is an mvel > feature. > > --- On Sun, 3/1/09, Edson Tirelli <tirelli(a)post.com&gt; wrote: > > > From: Edson Tirelli <tirelli(a)post.com&gt; > > Subject: Re: [rules-users] Creating objects in WHEN clause > > To: greg_barton(a)yahoo.com, "Rules Users List" < > rules-users(a)lists.jboss.org&gt; > > Date: Sunday, March 1, 2009, 12:46 PM > > 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 > > > > -- Edson Tirelli JBoss Drools Core Development JBoss, a division of Red Hat @ www.jboss.com