[rules-users] Rule using accumulate

[Andrés Corvetto]

Hi guys,

I'm new to drools, and i'm trying to build a small prototype.
I have 2 entities in my model: Offers and Bids. Both have a size (and a
price). I need a rule that matches a single Bid with multiple Offers adding
up in size to the Bid size. Matched Offers have to be sorted
by (increasing) insertion time .
I have managed to write a rule using 'accumulate', but i feel it's not too
efficient, since i have to match every Offer in the working memory with the
right price, sort them and then pick the first n ones.

Here's the rule:

rule "Match Bids"
when
$b : Bid($s:size, $p:price)
 $i : OfferAccumulator(acumSize >= $s) from accumulate ( $o:Offer(price<=$p)
,
init(OfferAccumulator accum = new OfferAccumulator($s); ),
 action( accum.add($o);),
reverse ( accum.remove($o);),
result( accum ))
 then
System.out.println( "Matched Bid:" + $b + "," + $i.getOffers());
end

and here's OfferAccumulator:

public class OfferAccumulator {
private int sizeLimit=0;
 private int accumSize=0;
 Set<Offer> offers = new TreeSet<Offer>();

public OfferAccumulator(int sizeLimit) {
this.sizeLimit = sizeLimit;
 }

public void add(Offer op) {
accumSize+=op.getSize();
 offers.add(op);
}

public void remove(Offer op) {
 if (offers.remove(op)) {
accumSize-=op.getSize();
}
 }

public List<Offer> getOffers() {
List<Offer> ret = new ArrayList<Offer>();
 int accum=0;
 Iterator<Offer> it = offers.iterator();
 while (it.hasNext() && acum<sizeLimit) {
Offer offer = it.next();
 accum+=offer.getSize();
ret.add(offer);
}
 return ret;
}
}

Can you think of a more efficient way of achieving the same result? Is there
a way of controlling the order in which facts are feeded to the accumulator?
Thanks in advance!
     Andres
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