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

[Wolfgang Laun]

On 18/02/2013, pdario <dario.piantanida at gmail.com> wrote:
> laune wrote
>> There is always just one fit; it just seems that there are multiple
>> fits - when you define your individual cases sloppily.
>
> Well, this is an assumption to get a completely disjointed classification,
> but this is not my case.
>
> I have a first level discount if you pay online and a second level discount
> if you pay online AND buy a special product.
>
> So, the second is true only if the first is.

Not *quite* correct: you have 1st level discount if you pay online and
DO NOT buy a special product.

>
>
> laune wrote
>>> when
>>>   Cart ($items : buyingItems, payment == Card....)
>>>   i : Item (code == XXXXX) from $items
>>> then
>>
>> I don't see why "XXXXX" shouldn't come from a parameter fact.
>>
>> As a general strategy, I try to avoid the "on-the-fly" objects
>> available with "from" and prefer these subordinate items to be
>> properly inserted facts. Usually this simplifies writing rules.
>
> If I simply put several carts and the whole items form them into memory, it
> would create a mess of carts and items, won't it?
> What will keep each item with its own cart?
>

a) Add a reference to its cart to each item.
b) Add facts CartItem( Cart cart, Item item)
c) Use the contains operator to establish an Item being part of a
cart's item list

-W