[rules-users] Accepted idiom for binding variable to restriction?

[Giovanni Motta]

Why not use from? The manual suggest this approach to reason over data that
is not explicitly asserted in knowledge base. It seems to me that it fits
best in the requirement of Laird. Please correct me if this is bad practice:
$response: Response()
$question: Question(ID == "XYZ") from $response.question

Is there some advantage/disadvantage on using 'from' instead of 'eval' in
this case?

Regards.
Giovanni
2010/6/2 Edson Tirelli <tirelli at post.com>

>
>    Syntactically speaking, I don't think the eval is necessary:
>
>   $response : Response( $question : question, question.ID == "XYZ" )
>
>    Behind the scenes Drools will still generate an eval to resolve the
> nested property constraint, but the rule stays simple to read and maintain.
>
>    Edson
>
> 2010/6/2 Wolfgang Laun <wolfgang.laun at gmail.com>
>
> The "inline eval" constraint is what you want: a boolean expression,
>> within parentheses.
>>
>>   $response : Response( $question : question,
>> eval(question.getID().equals( "XYZ" ) ) )
>>
>> See the Drools Expert manual, section on "Left Hand Side..."
>>
>> -W
>>
>>
>> On 1 June 2010 23:54, Laird Nelson <ljnelson at gmail.com> wrote:
>>
>>> I have a fact that is inserted into my rule base.  It is a Response.
>>>
>>> A Response has a Question that it is a response to.  At the moment,
>>> the Question itself is not separately inserted into the knowledge
>>> base.  I would ideally like to keep it this way.
>>>
>>> What's the best approach for binding variables to both the Response
>>> and its associated Question?
>>>
>>> That is, if the Question were inserted, it would be relatively easy:
>>>
>>> when
>>>  $question : Question( )
>>>  $response : Response( question == $question )
>>>
>>> ...but I'm finding myself somewhat confused how to "extract" a
>>> Question out of a Response, particularly when, say, I want to "select"
>>> only Responses whose associated Question IDs are "XYZ":
>>>
>>> when
>>>  $response : Response( $question : question.ID == "XYZ" ) // boy
>>> howdy does this seem wrong
>>>
>>> Is the easiest thing to do here to add a second rule that just inserts
>>> the questions:
>>>
>>> when
>>>  $response : Response
>>> then
>>>  insert($response.getQuestion())
>>> end
>>>
>>> ...?  I would love to stay away from this if I could.
>>>
>>> Thanks,
>>> Laird
>>> _______________________________________________
>>> rules-users mailing list
>>> rules-users at lists.jboss.org
>>> https://lists.jboss.org/mailman/listinfo/rules-users
>>>
>>
>>
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>>
>>
>
>
> --
>  Edson Tirelli
>  JBoss Drools Core Development
>  JBoss by Red Hat @ www.jboss.com
>
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>
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