ksession.execute(document);

I suppose this inserts a single EventRulesDocument object.

Here is the rule:

package sample1

import sample1.bean.EventRulesDocument;
import sample1.bean.Transaction;
import java.util.Date;

rule "Standard processing rule"

when
$doc : EventRulesDocument(
ruleRun == false && # <<< Wolfgang
event != null && event.eventType.eventCode == "testevent" )
then

Transaction t = new Transaction();
t.setEvent($doc.getEvent());
t.setCategory($doc.getEvent().getEventType().getEventCode());
t.setTransactionAmount($doc.getEvent().getEventAmount());
t.setCreateTs(new Date());
t.setUsername($doc.getEvent().getCreateUsername());

modify( $doc ) {setRuleRun(true)}; # Wolfgang <<<<<<
modify( $doc ) {addSaveTransaction(t)} ;

Here it is: You modify the EventRulesDocument, which causes another
activation of the same rule. One way of avoiding this is to add the rule
attribute no-loop true; another one is what you've done.

This isn't going to be your only rule?? This one alone is scant reason to use an RBS.

fireAllRules( 1 ) isn't a good remedy, because (normally) a Production System
relies on repeated firings, depending on rules and facts.

end

Additionally If any code in the world can be executed in the RHS, then
why shouldn't I just use groovy as my rule language? At least then, I
can write math like such:
def num1=95;
def num2=90;
def num3=num2/num1;

and all of the math is done with big decimal objects. IF there is no
restriction on what can be done in the RHS what is the advantage to
using a rules engine over a general purpose scripting language?

There is a good section in the Drools Expert manual: "Why use a rule engine?".
Don't do it just to be trendy ;-)

The
whole purpose for me choosing drools over Groovy eval() was that I
didn't want to give my users the ability to spawn threads, allocate
massive amounts of memory etc.

Seriously now, a Domain Specifiy Language is the maximum corset you can
force upon your users. But you'll have to know all they may do, and all the
conditions.

-W

On 09/18/2010 10:59 AM, Wolfgang Laun wrote:
> On 18 September 2010 16:15, Matt Young <solid@youngdev.net

> <mailto:solid@youngdev.net>> wrote:
>
> I just started using drools and this is my first time implementing
> a rules engine. Everything has been pretty smooth but I have
> some quirks that I am not sure I can live with. 1) for some reason,
> if I execute the Knowlege session against an object, the knowlege
> session never returns.
>
>
>> I don't understand the term "execute...against an object". Do you
>> mean that you have just one fact inserted befor you call
>> fireAllRules()?
>
>> But anyway, this call not returning is almost certainly due to a
>> loop in your rules, or have you made sure that they don't?
>
>
> The only way I can get the ksession to return is to make IF (obj ==
> null) part of the LHS and make modify($input){setObj("complete")}
> part of the RHS This seems like a deficiency since I have users
> writing their own rules, I can see them forgetting this
> requirement.
>
>
>> Writing rules is programming, no holds barred :-)
>
>> Look into Domain Specific Languages (DSL) as a cushion for the
>> unwary.
>
>
>
> IS their a way to get the ksession to firerules only once? If so
> what does that look like?
>
>
>> kSession.fireUntilHalt( 1 );
>
>
> 2) It seems that any code I want can be executed in the RHS. I
> could literally execute something like the following in the RHS.
>
> byte[] b= new byte[10000000000000]; // Really big memory waste
>
> I also could just start a bunch of threads.
>
> The point is that I am intending to let the users write their own
> rules but I can't do that if there are no restrictions on how/what
> can be done inside the rules. Any suggestions? Are there
> sandboxes or filters I can activate to restrict the RHS?
>
>
>> Again: DSL.
>
>> Also, Rule Templates might be the starting point; it'd depend on
>> what the may be allowed to do.
>
>> And what about good old-fashioned training?!
>
>> -W
>
>

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- --

Cheers,
Matt Young
solid@youngdev.net
http://youngdev.net

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