Re: [rules-users] calls to 'Helper' classes in LHS - are they allowed?
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(a)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(a)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(a)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
> > _______________________________________________
> > rules-users mailing list
> > rules-users(a)lists.jboss.org
> > https://lists.jboss.org/mailman/listinfo/rules-users
> >
>
>
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>
>
--
Steven Williams
Supervising Consultant
Object Consulting
Office: 8615 4500 Mob: 0439 898 668 Fax: 8615 4501
stevenw(a)objectconsulting.com.au
www.objectconsulting.com.au
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