Drools报错：Unable to find @positional字段，规则引擎新手求助

Hey there! Let's figure out how to fix that "Unable to find @positional field" error you're getting with your Drools rule. I've looked over your DRL code and there are a few key issues and checks we can do to resolve this.

First, spot the obvious syntax gaps in your rule #

Looking at your then block, two syntax issues are likely contributing to the error:

• You're missing a semicolon at the end of float totalBalance = getTotalBalance($node)
• The modify($node)... statement is incomplete. Drools needs explicit details on which field you want to update in the Person object.

Fix the rule syntax first #

Here's a corrected version of your rule with proper syntax:

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); // Added missing semicolon
 modify($node) {
     setTotalBalance(totalBalance); // Explicitly call the setter for the total balance field
 };
end

Now, check your Person domain class #

The "positional field" error often pops up when Drools can't properly access fields in your domain objects. To fix this:

• Make sure your Person class follows JavaBean standards: it should have a setTotalBalance(float) method (and a corresponding getTotalBalance() if you plan to use this field in other rules). For example:

public class Person {
    private boolean active;
    private List<Account> accounts;
    private float totalBalance;

    // Getters and setters
    public boolean isActive() { return active; }
    public void setActive(boolean active) { this.active = active; }
    public List<Account> getAccounts() { return accounts; }
    public void setAccounts(List<Account> accounts) { this.accounts = accounts; }
    public float getTotalBalance() { return totalBalance; }
    public void setTotalBalance(float totalBalance) { this.totalBalance = totalBalance; }
}

• If you were trying to use Drools' positional parameter syntax (e.g., modify($node, totalBalance)), you need to add the @Positional annotation to your Person class:

import org.drools.positional.Positional;

@Positional
public class Person {
    // ... rest of your class code ...
}

That said, using standard setter methods is the more common and maintainable approach for most cases.

Quick troubleshooting recap #

1. Fix all syntax errors in your DRL (missing semicolons, incomplete modify blocks)
2. Verify your Person class has the required getters/setters for fields you're modifying/accessing
3. If using positional parameters, add the @Positional annotation to your domain class

内容的提问来源于stack exchange，提问作者Arunkumar Mathiyazhagan