Drools Error : Unable to find @positional field

Question

I created a drool file PersonTotalAccountsBalance.drl as below. I am beginner in the rules engine world.

package com.auhuman.rules;

import com.auhuman.Person;
import com.auhuman.Account;

function float getTotalBalance(Person person) {
     float totalBalance = 0;
     for (Account account : person.getAccounts()){
         totalBalance += account.getBalance();
     }
     return totalBalance;
}

rule "PersonTotalAccountsBalance"
    when
        $node : Person(active == true)
    then
        float totalBalance = getTotalBalance($node)

        modify($node) {
           setTotalBalance(totalBalance);
        }
end

Upon compile I am getting below error

Unable to compile the file: PersonTotalAccountsBalance.drl. Errors = [Unable to find @positional field 0 for class Person
 : [Rule name='PersonTotalAccountsBalance']
]

Answer 1

Although this question is very old: I had the same error message but I was working with decision tables in xls (excel) format. The table looked like this:

Note that $order:Order is in a merged cell goes across both the CONDITION and the ACTION columns. That cell is only allowed to be above CONDITION tables, not the ACTION tables. After unmerging I didn't get the error anymore:

I got a very similar error when defining the wrong values in the ACTION column for setting an attribute. When using values without quotes for a String attribute in the model Order I got the following error:

Unable to get KieModule, Errors Existed: Error Messages:
Message [id=1, kieBase=defaultKieBase, level=ERROR, path=status_rules/status.xls, line=21, column=0
   text=Rule Compilation error The method setNextStatus(String) in the type Order is not applicable for the arguments (int)]
Message [id=2, kieBase=defaultKieBase, level=ERROR, path=status_rules/status.xls, line=5, column=0
   text=Rule Compilation error The method setNextStatus(String) in the type Order is not applicable for the arguments (int)]
Message [id=3, kieBase=defaultKieBase, level=ERROR, path=status_rules/status.xls, line=13, column=0
   text=Rule Compilation error The method setNextStatus(String) in the type Order is not applicable for the arguments (int)]

However in this case the error message was more precise.