[rules-users] Evaluate rules for multiple facts of the same type within a StateuflSession

[Wolfgang Laun]

See a few comments at the end.

rule "assign discount"
when
    $c: Cart( discount == null, $on: online, $citems: items, $age:
age, $shipping: shipping )
    $p: Param( online == $on, $pdisc: discount, $pitems: items,
               minage <= $age,
               shipping == Param.NA_SHIPPING || == $shipping,
               eval($citems.containsAll($pitems)) )
    not Param( online == $on, discount > $pdisc, $xitems: items,
               minage <= $age,
               shipping == Param.NA_SHIPPING || == $shipping,
               eval($citems.containsAll($xitems)) )
then
    modify( $c ){
        setDiscount( $pdisc )
    }
end

* To revert the Cart to discount == null etc., use another rule,
triggered by a "command" fact, which is retracted by the very same
rule.

* items is a Set<String> which can be easily maintained in addition to
a List<Items>. Or add methods supporting the required set operations,
computing the Set<String> on the fly.

* Note the use of a dedicated value for "don't care", e.g. NA_SHIPPING.

* An entirely new criteria will have to be accomodated in the (single)
rule, but the example covers discrete values and sets; take care when
there could be ranges, as with age.

-W





On 19/02/2013, pdario <dario.piantanida at gmail.com> wrote:
> laune wrote
>> I'm confident that there's a clean and manageable way of preparing
>> this data to work in combination with a small and constant set of
>> rules.  I refrain from elaborating this in all details without knowing
>> all of the requirements.
>
> I'll try to summarize them as properly as I can...
>
> Rule 0: default condition
> If cart is paid "offline", it has 0% discount
>
> Rule 1: online payment discount
> If cart is paid "online", it has 10% discount
>
> These two are fixed and always valid.
>
> Then we monthly decide a list of items that grant different discounts on
> the
> whole cart over the 10% of Rule 1 (i.e. Rule 1 must be true to get further
> discount).
>
> For example:
> Rule 2: valid for February 2013, item A
> If cart is paid "online" and contains item A, it has 15% discount
> Rule 3: valid for February 2013, item B
> If cart is paid "online" and contains item B, it has 17% discount
>
> Next month, both items and discount levels will change
>
> We need the firt Rule 0 because the user can change the payment method, so
> we have to reset the discount to 0.
>
> Ideally, we would like to left the Rule 0 and 1 unchanged (as they are
> basic
> rule) and manage the monthly rules without impact on them.
>
> To make things worse, our business people not only rely on items contained
> in the cart, but each month they decide a different attribute from the cart
> or user to be taken into account for special discount, so that the examples
> above may read like:
>
> Rule 2: valid for February 2013, item A
> If cart is paid "online" and contains item A and the user is older than 30,
> it has 15% discount
> Rule 3: valid for February 2013, item B
> If cart is paid "online" and contains item B and the cart is shipped within
> Europe, it has 17% discount
>
> As you remember, we used salience and activation groups, but this prevents
> us from applying rules to a bunch of carts, as the rule activation cancels
> other activations.
>
> Do you see a cleaner design?
>
> Thank you a lot for support.
>
>
>
> --
> View this message in context:
> http://drools.46999.n3.nabble.com/Evaluate-rules-for-multiple-facts-of-the-same-type-within-a-StateuflSession-tp4022157p4022441.html
> Sent from the Drools: User forum mailing list archive at Nabble.com.
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