[rules-users] calls to 'Helper' classes in LHS - are they allowed?

[Michael Suzio]

I see this in the docs:

"A Predicate constraint can use any valid Java expression as long as it
evaluated to a primitive boolean - avoid using any Drools keywords as
Declaration identifiers. Previously bound declarations can be used in the
expression. Functions used in a Predicate Constraint must return time
constant results."

and under the discussion of 'eval':

"Evals cannot be indexed and thus are not as optimal as using Field
Constraints."

and this in general discussion of constraints and accessors of your objects
used in them:

"Do please make sure that you are accessing methods that take no parameters,
and are in-fact "accessors" (as in, they don't change the state of the
object in a way that may effect the rules - remember that the rule engine
effectively caches the results of its matching inbetween invocations to make
it faster)."

So, if invoking a helper method is like an eval, I'm thinking Drools
computes the match, but then throws it away because it knows this is not a
constant expression.  Whereas, if it were just a match of an accessor's
value vs. a constant String, it could cache that.

I'm wildly speculating, only because I want to understand fully what is
happening, so I'm throwing stuff out there so the Drools team will have to
correct my misapprehensions before I confuse the whole list (*g*).
Sometimes reading the Drools documentation is like a Talmudic scholar trying
to find the deeper meaning of the sacred words...  as much as I want
the 3.2milestone, I want real documentation even more (and *hint hint*
-- would
probably be willing to pay for it, guys!  Can we get an O'Reilly book?)

  --- Michael

On 2/12/07, Steven Williams <stevenw at objectconsulting.com.au> wrote:
>
> I believe there is a caveat on functions and helper methods called from
> the LHS that they need to be constant over time (or at least over the life
> of the working memory) which then allows matches to be computed as per
> normal.
>
> Steve
>
> On 2/13/07, Michael Suzio <msuzio at gmail.com> wrote:
> >
> > The JBoss guys can correct me if I'm wrong, but although I think that
> > works, what you've just done is eliminate any chance to precompute matches
> > and trim down the checks that need to happen to find a rule match.  Since
> > the engine can't know that Helper.transform("value") returns a constant
> > value, it has to re-run that every time and it has to reject for matches to
> > the rule constraint every time.
> >
> > I'm sure this would really sink performance, in other words.  You can
> > easily see the effect -- write the rule this way and time it, and then write
> > it with the return value of Helper.transform being inlined, and I'm sure
> > there's a big difference.  It's the same as any other eval(...) situation in
> > Drools; possible, but not good for performance.
> >
> > On 2/12/07, Olenin, Vladimir (MOH) <Vladimir.Olenin at moh.gov.on.ca>
> > wrote:
> > >
> > > Hi,
> > >
> > > I was wondering if calls to a Helper class are allowed in LHS of the
> > > rule?
> > > Eg:
> > >
> > > Rule myRule
> > > When
> > >         MyObject(objField == Helper.transform("value"))
> > > Then
> > >        // smth
> > > End
> > >
> > >
> > > Thanks,
> > >
> > > Vlad
> > > _______________________________________________
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> > > rules-users at lists.jboss.org
> > > https://lists.jboss.org/mailman/listinfo/rules-users
> > >
> >
> >
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> >
> >
>
>
> --
> Steven Williams
>
> Supervising Consultant
>
> Object Consulting
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