[rules-users] Fact Instance "lifetime" in knowledge session

[Anne Fiore]

Hi,

I'm very new to drools and am trying to understand how "facts" are managed
by the knowledge session.  I've been experimenting with a simple example
using drools 5.3.0.  I created a simple Account class that has a single
"balance" attribute.  My rule tests the balance and prints a message if it
is less than 100. I am creating a new instance of Account in my main method
and inserting it into a stateful knowledge session.   I put this into a
loop that runs 3 times and never dispose of the session.  Each of my
Account instances has a balance less that 100.  Here is a portion of the
code:

    public static final void main(String[] args) throws InterruptedException
    {
        KnowledgeBase knowledgeBase = createKnowledgeBase();
        StatefulKnowledgeSession session =
knowledgeBase.newStatefulKnowledgeSession();

        for (int i = 0; i < 3; i++)
        {
            try
            {
                Account account = new Account();
                switch (i)
                {
                   case 0: account.setBalance(95);
                           break;
                   case 1: account.setBalance(85);
                           break;
                   case 2: account.setBalance(80);
                           break;
                   default: account.setBalance(80);
                }
                session.insert(account);
                session.fireAllRules();
            }
            catch (Exception e)
            {
                System.out.println("Exception: " + e.toString());
            }
            Thread.sleep(1000);
        }
    }

My rule is:
rule "basic rule"
when $a : Account (balance < 100) // condition
then System.out.println("Account balance " + $a.getBalance() + " is less
than 100");  // consequence
end

What I see is that each time the loop executes only the last instance of
Account seems to get triggered.  I expected that each time I call
"fireAllRules" it would examine all the facts in the session and execute
them. So I thought the first time the loop runs I would get 1 activation,
the second time the loop runs I get 2 activations, etc.

Are all 3 instances of Account still in the working memory or is the latest
instance replacing the existing one?  Or, once a fact triggers the rules
engine, does it not trigger it again?

Thanks for any insights,
Anne
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