Re: [rules-users] Newbie question on accessing predecessor and successor in a list
Thanks Greg for your fast reply. Unfortunately I do not get this to work:
$preSegment : Segment (
$journey.segmentList.indexOf(this) ==
($journey.segmentList.indexOf($segment) - 1),
countries not contains Country.Switzerland && ...
) from $journey.segmentList
Compiler throws:
[36,48]: unknown:36:48 Unexpected token 'this'[36,98]: unknown:36:98
Unexpected token '$segment'
Is it possible to use eval() inside Segment ()?
With eval the compiler throws something like this:
$journey.segmentList cannot be resolved to a type
Cannot use this in a static context
I don't know how matching works in drools, but wouldn't this also be very
expensive? As for every match of Segment ( ) the segmentList has to be
iterated two times. These lists can get very long. A cheap approach would be
if the from statement would "know" the index of the Segment () matched. I
was hoping this would be possible.
Regards,
Chris
Greg Barton wrote:
You can't do $journey.segmentList.indexOf(this) and
$journey.segmentList.indexOf($segment), even in an eval?
--- On Mon, 11/3/08, CSchr <christian.schrinner(a)sbb.ch> wrote:
> From: CSchr <christian.schrinner(a)sbb.ch>
> Subject: [rules-users] Newbie question on accessing predecessor and
> successor in a list
> To: rules-users(a)lists.jboss.org
> Date: Monday, November 3, 2008, 9:56 AM
> Hi everyone!
>
> I'm relatively new to Drools and rule languages.
>
> I'm wondering if it is possible to access the
> predecessor and successor in a
> match using from operator on an (Array)List. I have
> something like this
> (simplified):
>
> ...
> $segment : Segment( countries contains Country.Switzerland
> && ... ) from
> $journey.segmentList
>
> $preSegment : Segment ( indexOf(this) == indexOf($segment)
> - 1,
> countries not contains Country.Switzerland
> && ...
> ) from $journey.segmentList
>
> I need something like indexOf() for the exact predecessor
> of the matched
> segment.
>
> If the matched business object was an element of a double
> linked list it
> would be easy. Unfortunately I don't have the luxury to
> change the business
> object into knowing it's predecessor or successor. I
> have to prove that we
> could write our java coded business rules in Drools rule
> language without
> changing the business object model.
>
> Thanks in advance,
>
> Chris
>
>
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