[rules-users] Collecting all items of nested collections / accumulate nested collections

[Claes, Kenny [JRDBE - Non J&J]]

I have a question regarding creating a list of items that are all in
nested collections of my main object.
A high level overview of the model is like this:
 
public Level0 { 
 private List<Level1> level1List; 
} 
 
public Level1 { 
 private List<Level2> level1List; 
} 
 
public Level2 { 
 private Date occurence; 
} 
 
Now, I add objects of type 0 in the working memory and for each of those
objects, I want to find the latest occurrence of a certain Level2,
regardless of which level1 they belong to.
 
If there's only 2 levels and I want to find the latest occurrence of
Level2's with a certain name, I can write:
 
rule "latest level 1"
when
    $l0: Level0()
    $date: Date() from accumulate (Level1(name in ("name1", "name2"),
$occurence: occurence) from $l0.level1List, maxDate($occurence)) 
then
      // register fact that latest occurrence of name1/name2 level1 was
on $date
end
 
Now, with 3 levels, since I obviously can't replace $l0.level1List with
$l0.level1List.level2List, is there a way to create an intermediate list
that will contain all Level2 objects? No filtering needs to take place
on Level1, but if there's a way to do that too, that would be nice.
 
What I currently have is this:
 
rule "latest level 2"
when
$l0: Level0()
$l1: Level1() from $l1.level1List
$l2List: List(size > 0) from collect( Level2(name in (("name1",
"name2")) from $l1.level2List )
      $date: PartialDate() from accumulate (Level2( $occurence:
occurence) from $l2List, maxDate($occurence))
then
      // register fact that latest occurrence of name1/name2 level2 was
on $date
end
 
But this does not work as it treats each Level1 seperately: it creates a
"latest occurrence" for all accumulated level2 facts within a level1,
instead of one for the entire set of level 2's 'owned' by the level0
object.
 
Any suggestions?
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