[rules-users] Newbie question on accessing predecessor and successor in a list

[CSchr]

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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