On 06/08/2010 16:04, Anstis, Michael (M.) wrote:
HI,
There was an interesting discussion today on IRC; a user "jochen"
reported NPEs when trying to iterate lists in the RHS constructed in
the LHS using "from collect".
I was wondering how Drools handles lists constructed in the LHS; if
the list contained 5 elements but another rule retracted one of those
elements would the list available in the RHS contain 4 or 5 elements?
Here's a simplification of what was posted at
_http://pastebin.com/yKGSxFkA_
Rule 1
when
$cheese : ArrayList() from collect(CheeseFact());
then
for(int i=0; i<$cheese.size(); i++) {
//Something useful...
}
end
What if there was another rule that did something like this:-
Rule 2
When
$cf : CheeseFact(type == "chedder")
Then
retract($cf);
end
Each time this "rule 2" fires and retracts a CheeseFact that was in
$cheese from rule1, the $cheese list will be reduced by one. So there
should be no null pointers here.
Mark
What would be the list Rule 1 iterates?
I'd assume since I believe activation execution to be serial it would
depend on the agenda's conflict resolution strategy or rule salience?
What would be the learned opinion?
With kind regards,
Mike
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