The email is big just because I tried to big as clear as possible, but it's a quick reading, I promise!

No one?


On Tue, Nov 24, 2009 at 10:42 PM, Leonardo Gomes <> wrote:

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"
    not FactA( id == 4 )
    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.


2009/11/17 Edson Tirelli <>


   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.


2009/11/17 Leonardo Gomes <>
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"


SiteLanguage(language : languageCode)
t : SiteSpecialServiceType(type : specialServiceType)
not SiteLanguageSpecialServiceType(specialServiceType == type, languageCode == language)

How could I solve or workaround that?

Thanks in advance,
rules-users mailing list

 Edson Tirelli
 JBoss Drools Core Development
 JBoss by Red Hat @

rules-users mailing list