[rules-users] bug or feature not yet implemented

[Manukyan, Sergey]

Thank you Edson,

 

I am not a developer of drools, so I appreciate your sharing of design
decisions here.

 

I still wish the "field constraint" be a field constraint no matter how
this field is referenced, be it by name or by variable that references
this field, otherwise it is more like "field name constraint"

 

So I wish I could do:

 

Person( 

            $a : age,

            $minAge : 30,

            $maxAge : 40,

$a > $minAge && < $maxAge)

 

The introduction of local variable can be helpful when field names are
complex and long (that is the case I have now), and need to be used more
then once inside of expression. Also using eval involves performance
penalty, so I would like to avoid it wherever possible,

 

Just my 2 cents...

 

-Sergey

 

 

 

 

 

________________________________

From: rules-users-bounces at lists.jboss.org
[mailto:rules-users-bounces at lists.jboss.org] On Behalf Of Edson Tirelli
Sent: Friday, August 10, 2007 3:17 PM
To: Rules Users List
Subject: Re: [rules-users] bug or feature not yet implemented

 


   Sergey,

   Well, a "field constraint" must always involve a field. The decision
to have it on the left side is to simplify syntax. For instance, if you
want to write something like: "age between 30 and 40", you can do: 

Person( age > 30 && < 40 )

    So you declare the field only once and can have as many expressions
applied over it as you want, using restriction connectives (&& and ||).

    Now, if your expression does not involve a field, then it is not a
"field constraint". It may be an "inline-eval" (previously called
predicate expression) for instance. And in this case, you use the "eval"
keyword as showed in my previous example. 
    Unfortunatelly, to avoid language ambiguities, we can't support
arbitrary expressions without a markup keyword, and "eval" was the
chosen keyword.

    []s
    Edson

2007/8/10, Manukyan, Sergey <SManukyan at lear.com>:

Thanks Edson for workaround,

 

IMHO that looks like a limitation to me, is there a particular reason
why left side should always be a field?

 

-Sergey

 

 

________________________________

From: rules-users-bounces at lists.jboss.org
[mailto:rules-users-bounces at lists.jboss.org] On Behalf Of Edson Tirelli
Sent: Friday, August 10, 2007 11:58 AM
To: Rules Users List
Subject: Re: [rules-users] bug or feature not yet implemented

 


   Sergey,

   That is how it is supposed to work. A field constraint in Drools
always has a field at its left side. If you want arbitrary expression,
just embed it in an inline eval:

        S : Supplier( 
                $sts  : supplierBusinessStatus.businessStatus,
                $csts :
corporateSupplier.supplierBusinessStatus.businessStatus,                
                eval ( $sts != $csts )  
        ) 

   Although, for this specific case, it would be better (more
performatic) to simply write:

        S : Supplier(
                $sts  : supplierBusinessStatus.businessStatus,
                $csts :
corporateSupplier.supplierBusinessStatus.businessStatus != $sts
        )

    []s
    Edson

2007/8/10, Manukyan, Sergey <SManukyan at lear.com >:


Folks,

I found that drools 4.0GA doesn't recognize variables in the left side
of operator expression

Like this produces error:


When
        S : Supplier(
                $sts  : supplierBusinessStatus.businessStatus ,
                $csts :
corporateSupplier.supplierBusinessStatus.businessStatus,
                $sts != $csts
                )
Then
        ...



It tries to treat the $sts variable as a field of Supplier, instead 
understanding that it is a variable declared earlier,

Please advise,

Thanks,

-Sergey




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-- 
  Edson Tirelli
  Software Engineer - JBoss Rules Core Developer
  Office: +55 11 3529-6000
  Mobile: +55 11 9287-5646 
  JBoss, a division of Red Hat @ www.jboss.com 


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rules-users mailing list
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-- 
  Edson Tirelli
  Software Engineer - JBoss Rules Core Developer
  Office: +55 11 3529-6000
  Mobile: +55 11 9287-5646 
  JBoss, a division of Red Hat @ www.jboss.com 

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