[rules-users] Roll Back Rule / Rule Transactions?

[Michael Suzio]

Anytime you modify a object, candidate rules are going to be re-examined.
You may need some state variables in addition to this (to control when rules
fire, avoid loops, etc), but the basic rules could be:

rule AddVcr
when
  $c: Cart(contents contains "TV", contents excludes "free VCR")
then
 $c.add("free VCR");
 modify($c);
end

rule RemoveVcr
when
 $c: Cart(contents excludes "TV")
then
 $c.remove("free VCR");
 modify($c);
end

You can fill in the rest.  Like I said, you probably need some state
variables so things don't loop, need to exclude the case where a non-free
VCR is legitimately in the cart, etc.  But your basic question should be
answered with this approach.  Don't think procedurally, think in terms of a
living system when the changes in objects trigger somewhat asynchronous
cascades of matching rules.  Calling modify() on a fact is like restarting
the whole matching algorithm for any rules that had that fact included in
their (possible candidate) constraints.

On 2/13/07, Matt Johnston <MJohnston at pubgroup.com> wrote:
>
> I am working on rules for an online shopping cart. Depending on the
> products in the cart, the customer may get certain discounts.
>
> If cart contains a TV, add a free VCR.
>
> I can apply these rules, but what about rolling them back?
>
> So in the example above, the rule automatically added a free VCR because
> the cart contained a TV. If the customer removes the TV, I need to roll
> back the VCR rule and also remove the VCR from the cart.
>
> Does anyone know how to do this? Is it possible?
>
> Matt Johnston
> Manager of Internet Content
> Publishing Group of America
> p: 615-468-6053
> f: 615-468-6153
>
> _______________________________________________
> rules-users mailing list
> rules-users at lists.jboss.org
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>
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