Hi,
I am new to drools, trying to see if I could use it to implement a
discount engine.
I am playing with the petstore example (shopping cart), and I was
wondering if Drools has a pattern matching feature or not, if rules can
be fired based on combinations rather than permutations.
For example I want to implement a buy 2 Gold Fishes get 1 free discount.
If I define my rule like:
<java:condition>item1.getName().equals( "Gold Fish" )</java:condition>
<java:condition>item2.getName().equals( "Gold Fish" )</java:condition>
<java:consequence>
//gives 100% discount to one item
item2.setDiscount(100);
</java:consequence>
If the user puts 2 Golf Fishes in his cart (A, B), the rule will fire 4
times (for permutation (A,A), (A,B), (B,B), (B, A), and gives 100%
discount to all items...That does not work.
I can add a condition to make sure the items are different and the rules
fires only once per combo such as
<java:condition>item1.getId()>item2.getId()</java:condition>
That works in this case, but it is not scalable at all (if I want to do
4 gold fishes get 1 free...it gets more complicated).
I also want the rule to fire more than 1 time if the user has let's say
8 gold fishes (he should get 4 free), so having a condition on the cart
itself such as cart.hasXitems(4, "GolfFish") would probably not work I
suppose (such rule would be fired only once if I understand how the
engine works).
So how would this (buy X items, get 1 free; applicable more than 1 time
per cart) be implemented in a scalable and elegant way with drools?
Is there some kind of pattern engine in drools (not sure if this is the
proper term for this, but basically I want the rule to be fired only
once per combination of facts that match some conditions, not per
permutation..)?
Thanks.
Laurent
