[rules-users] Stateful session and non-existence of Facts

[Leonardo Gomes]

Hello,

Regarding the session recreation, you're absolutely right, thanks!

Anyway, I still have a problem and I believe it's more a design thing. Let
me try to clarify it.

I have different types of facts, let's say:

* Types: FactA, FactB, FactC;
* A stateful session with rules operating on them;
* And a global variable, called output, which is a list of messages
generated as consequences of those rules;
* From time to time, I get notified that a fact of type FactA changed, then
I have to:
  - retract all facts of type FactA from my working memory
  - reload them from the database (with java beans being created)
  - reinsert them in that stateful session

Now, let's say FactA(1) indicates a fact of type FactA and id = 1.

- Then, in the beginning, I insert FactA(1) and FactA(2) in my working
memory and fire the rules.
- I have several rules operating on different types of facts, but I'm
interested in one rule in particular which operates against FactA and reads
something like:

rule "test non existence"
when
    not FactA( id == 4 )
then
    output.add("there's no FactA id 4");

- This rule is fired and the message is added to my output object.

Later on, I have a notification that a FactA has changed, then I:
- retract all FactAs from my working memory
- clear all FactA-related messages from my output object
- reload FactAs (let's say now I have FactA(1), FactA(3), but NOT FactA(4))
- reinsert them in the WM
- fire the rules

The rule that checks that there's no FactA(4) doesn't refire. All other
rules operating against FactA do, and since I had removed all FactA-related
messages from my output object, this time I don't get the "there no FactA id
4" message in my output.

It sounds like a situation for a stateless session, but I actually have
several different rules, operating on different types of facts and don't
want to refire all rules, just because a fact of type A changed.

Maybe I should have an strategy of creating different sets of stateless
sessions. I'm not sure. Advice is really welcome!

Thanks again.

Leo.










2009/11/17 Edson Tirelli <ed.tirelli at gmail.com>

>
>    Leonardo,
>
>    First, I believer there is a misconception in your reasoning: creating
> sessions is supposed to be much much cheaper than retracting all facts.
> Creating a rulebase is heavier, because it requires compilation, but
> creating a session is supposed to be very light by design. So, first thing
> you should do is change that.
>
>    Regarding your question, if you insert:
>
>
> SiteLanguage(language : languageCode)
> t : SiteSpecialServiceType(type : specialServiceType)
>
>    The rule will activate and fire. If you don't, then the rule will not
> match. That is how it is supposed to work.
>
>    Edson
>
> 2009/11/17 Leonardo Gomes <leonardo.f.gomes at gmail.com>
>
>> Hi Guys,
>>
>> I have the following situation while running a stateful session with
>> Drools 4.0.7:
>>
>> - I want to test that a fact with a given state doesn't exist;
>> - It works fine
>> - At a certain point I have to retract all facts and reinsert them at the
>> stateful session - some of them actually changed and I don't want to
>> recreate the session b/c it's expensive
>> - Again the fact that didn't exist when I first created the session still
>> doesn't exist
>>
>> ** Problem: This time the rule that verified the non-existence is not
>> fired because I didn't insert any fact that would retrigger it.
>>
>> Rule example:
>>
>> rule "022"
>>
>> when
>>
>> SiteLanguage(language : languageCode)
>> t : SiteSpecialServiceType(type : specialServiceType)
>> not SiteLanguageSpecialServiceType(specialServiceType == type,
>> languageCode == language)
>> then
>>                 <<consequence>>
>> end
>>
>> How could I solve or workaround that?
>>
>>
>> Thanks in advance,
>> Leo.
>> _______________________________________________
>> rules-users mailing list
>> rules-users at lists.jboss.org
>> https://lists.jboss.org/mailman/listinfo/rules-users
>>
>>
>
>
> --
>  Edson Tirelli
>  JBoss Drools Core Development
>  JBoss by Red Hat @ www.jboss.com
>
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>
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