[rules-users] Creating objects in WHEN clause

[Edson Tirelli]

   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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.jboss.org/pipermail/rules-users/attachments/20090301/3e1bb945/attachment.html