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

[Wolfgang Laun]

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
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