Drools - Revert rule engine to initial state?

3
votes

Is there a way to revert rule engine ( stateful ) to initial state ( state where all rules and facts are inserted and fireAllRules() not been fired ) ?

Thanks in advance !

2
drools
Why not just create a new one then? :) – Adrian Shum
I have large number of facts. If i create a new knowledge session wouldn't i required to insert facts again. In my system I create statefull knowledge session once and fire all rules, get the results. For next operation i need knowledge session to be in initial state. – Viraj
It seems to me that you may change your design a bit to make use of Stateless session instead. Instead of insert facts to session, you create a list to store the facts. Then you can reuse your list of facts to have the Statless session execute against. – Adrian Shum
In my system some rules depend on other rules ( using modify block ). Therefore i can't use stateless session. – Viraj
Yes you can use a stateless session. Modify can be used there.. – salaboy

2 Answers

1
votes

There is no initial state in a session besides when it's created. When you insert Facts into the session the rules are evaluated, so you cannot go back into the evaluation steps. Maybe you can refactor your use case to make it perform better, but without more knowledge about your specific situation is very difficult to help you.

1
votes

I ran into the same problem.

Yes, if you create a new session you will need to re-insert your new facts. Supposedly creating sessions is fast, but I have not been forced to run performance tests (yet). If you don't want to recreate the session, you can just retract the inserted fact objects. And then re-insert them. (Note that the 'retract' method has been deprecated in favor of 'delete'). So my code for my toy problem looks like this (I "reset" the session three times):

System.out.println("--Load the knowledge base with rules.--");
KieServices kServices = KieServices.Factory.get();
KieContainer kContainer = kServices.getKieClasspathContainer();
KieSession kSession = kContainer.newKieSession("ksession-rules");
Account account = new Account(200, "Mickey Mouse");
account.withdraw(150);
kSession.insert(account);
int rulesFired = kSession.fireAllRules();
System.out.println("**** Finished first run, fired " + rulesFired + " rule(s).");

 // Reset session/rules by retracting facts
 FactHandle handle = kSession.getFactHandle(account);
 kSession.delete(handle);

 account.deposit(1000);
 kSession.insert(account);
 rulesFired = kSession.fireAllRules();
 System.out.println("**** Finished second run, fired " + rulesFired + " rule(s).");

 //Reset rules again
 handle = kSession.getFactHandle(account);
 kSession.delete(handle);

 account.deposit(10000000);
 kSession.insert(account);
 rulesFired = kSession.fireAllRules();
 System.out.println("**** Finished third run, fired " + rulesFired + " rule(s).");

 kSession.dispose();

You say that you have a "large number of facts". How large is large? (In my toy "Account" object, I have one String and one Integer). 100 BigDecimal fields? 100,000 Strings? Or are you referring to a large number of orders, implying that you need to "reset" the knowledge base many times per second?