All,

    Unfortunately the problem of dealing with a clock in a rules engine is a lot more complex than it seems at first.

    David, your best bet is to create an instance of a clock class, insert as a fact and update this fact from time to time when you want your rules to be reevaluated. Do not use any Calendar.getInstance() or System.currentTimeMillis() in the LHS of your rules, because you will get inconsistent behavior. Also, once you have the clock as a fact, I back the suggestion of using a library like JodaTime for date arithmetics.

    If you want to go the extra mile, you can implement your own operators in drools, but in Drools 4 this is still not as simple as in Drools 5.

    Just to reinforce, the problem is not handling dates themselves. The problem is constraining your rules against the concept of "current time" because that is mutable.

    Michael's idea of using collect/accumulate for counting days is creative, but unfortunately too heavy for practical uses I am afraid.

    Good luck,
       Edson

   

2009/1/29 Anstis, Michael (M.) <manstis1@ford.com>
You got it.
 
You won't find this proposal in any pattern books!! ;-)
 
At least you understood the syntax, so you can now officially consider yourself not a noob.

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of David Siefert
Sent: 29 January 2009 12:59

To: Rules Users List
Subject: Re: [rules-users] Working with dates in rules

Ah! Sorry, I believe you were saying Day is a fact that I would have to create for each likely day....  The collect operation is what gathers all those (Day) facts into a list that is counted. so the rule fires if there is more than 0 day facts.
 
My bad!
 
Thanks,
David

On Thu, Jan 29, 2009 at 6:53 AM, David Siefert <siefert.david.mailinglist@gmail.com> wrote:
Hey, that was quite clever.  Where can I find more about Day()?  I did some research about DateFactory which I can see how dates get parsed according to the documentation, as well as compared with the conditional operators (<, >, <=, >=, etc).
 
Thanks,
David

On Thu, Jan 29, 2009 at 5:57 AM, Anstis, Michael (M.) <manstis1@ford.com> wrote:
Hi David,
 
Sorry it was of little help.
 
A rule of thumb is to stay away from "eval" as it kills performance (the patterns can't be indexed).
 
I'm not sure if Drools can handle Date variables (the docs state it handles Data literals formatted as "dd-mmm-yyyy" so Cheese( date == "27-Oct-2008") works).
 
I guess you could look at something like this (gees, this is going to show how "green" I am with Drools now):-
 
rule "yuck"
    when
        DateFactory($today : today )
        $c : CreditCard( $expires : expirationDate )
        ArrayList( size >= 0 ) from collect( Day( date >= $today, date <= $expires ))
    then
        //Difference between "today" and "expiry date" is more than zero days
end
 
This does require the insertion of (possibly) huge amounts of Day facts. Yuck. There must be a better way (in fact your eval looks soooo much cleaner). I'm just throwing out ideas.
 
Good luck with your adventures with Drools.
 
Mike

Sent: 29 January 2009 11:31
To: Rules Users List
Subject: Re: [rules-users] Working with dates in rules

Not sure--Drools 5 temporal reasoning looks like it would be the answer.  Only problem is that I need a solution now, so I am stuck with Drools 4.
 
This did give me some ideas though.  I created myself a class called TemporalReasoner.  This has a few methods, namely to roll a date (so I can tell it x amount of time from now), and then compare it to another date.
 
So in my rule, lets say I have a fact CreditCard with property expiration:Date (speaking uml-ishly for "a property named 'expiration' of type Date"):
 
rule "Fires when expiration less than today"
  when
    $c: CreditCard($expires : expirationDate)
    eval(new TemporalReasoner(Calendar.getInstance()).lessThan($expires))
  then
    // do something for when credit card is still valid
end
 
Now, I'm still generally a noob with BRs, so I'm not sure how this will affect performance.  Any advice?
 
Thanks,
David

On Thu, Jan 29, 2009 at 3:50 AM, Anstis, Michael (M.) <manstis1@ford.com> wrote:
Hi,
 
I wonder whether Drools 5 "Complex Event Processing Support (Temporal Reasoning)" might be what you're looking for?
 
 
With kind regards,
 
Mike

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of David Siefert
Sent: 29 January 2009 09:40
To: Rules Users List
Subject: [rules-users] Working with dates in rules

Hi-
 
I'm wondering how it would be possible to compare a part of a date in the lhs condition of a rule in a Drool.  In other words, I need to compare a date to see if it is x days from the current date, n hours from current time, etc.  Would anyone be kind enough to provide an example?  I'm thinking I may have to implement something of my own to offer that functionality?
 
Big thanks,
David

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--
 Edson Tirelli
 JBoss Drools Core Development
 JBoss, a division of Red Hat @ www.jboss.com