Reuse part of Drools `when` statement

Question

I have bulk of Drools rules with the similar when parts. E.g.

rule "Rule 1"
    when
        trn: TransactionEvent()

        // some `trn` related statements

        not ConfirmEvent (
            processMessageId == trn.groupId )
    then
        // some actions
end

rule "Rule 2"
    when
        trn: TransactionEvent()

        // some other `trn` related statements

        not ConfirmEvent (
            processMessageId == trn.groupId )
    then
        // some other actions
end

Is it possible to define one time this statement

not ConfirmEvent (
    processMessageId == trn.groupId )

and reuse somehow where needed?

Answer 1

Two approach ideas:

1. Use the rule "extends" keyword with each rule to extend a base rule containing the shared when statements.

2. Create a rule with the shared when statements that infers a fact ("extract rule"). Use that fact in the when conditions of the rules needing the shared conditions. This option is typically my preferred approach as it defines a "concept" (a named fact) for those conditions and evaluates only once vs each rule.

   Rule example for #2:

   rule "Transaction situation exists"
       when
           trn: TransactionEvent()
   
           // some `trn` related statements
   
           $optionalData : // bind as wanted
   
           not ConfirmEvent (
               processMessageId == trn.groupId )
       then
           InferredFact $inferredFact = new InferredFact($optionalData);
           insertLogical($inferredFact);
   end
   
   rule "Rule 1"
       when
           InferredFact()
           AdditionalCondition()
       then
           // some actions
   end
   
   rule "Rule 2"
       when
           InferredFact()
           OtherCondition()
       then
           // some other actions
   end