[rules-users] Creating objects in WHEN clause

[Greg Barton]

Ah, I thought the LHS was parsed into mvel by default.  OK, my bad.

--- On Sun, 3/1/09, Edson Tirelli <tirelli at post.com> wrote:

> From: Edson Tirelli <tirelli at post.com>
> Subject: Re: [rules-users] Creating objects in WHEN clause
> To: greg_barton at 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/test/java/org/drools/base/EvaluatorFactoryTest.java
> 
>    Take a look at testObject().
> 
>    []s
>    Edson
> 
> 2009/3/1 Greg Barton <greg_barton at yahoo.com>
> 
> > 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 at post.com> wrote:
> >
> > > From: Edson Tirelli <tirelli at post.com>
> > > Subject: Re: [rules-users] Creating objects in
> WHEN clause
> > > To: greg_barton at yahoo.com, "Rules Users
> List" <
> > rules-users at lists.jboss.org>
> > > 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 at yahoo.com>
> > >
> > > > 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 at dbmotion.com> wrote:
> > > >
> > > > > From: David Boaz
> <davidb at dbmotion.com>
> > > > > Subject: Re: [rules-users] Creating
> objects in
> > > WHEN clause
> > > > > To: rules-users at 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 at 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