Rule Language

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Rule Structure Comparison

• Rule Declaration: Defines the rule name and optional attributes
• Conditions (LHS): The ‘when’ section that defines what conditions must be true for the rule to fire
• Actions (RHS): The ‘then’ section that defines what actions to take when the rule fires

rule "Rule Name"
// Optional attributes (salience, no-loop, agenda-group, etc.)
salience 10 // (1)
no-loop true // (2)

when
// Conditions (Left-Hand Side)
$customer: Customer(age > 18, status == "active")
    $order: Order(customer == $customer, total > 100) // (3)
then
    // Actions (Right-Hand Side)
    $order.applyDiscount(10); // (4)
    update($order);
System.out.println("Discount applied to order " + $order.getId());
end

1. Has a priority of 10 (higher than default)
2. Will not re-trigger even if its actions modify objects (no-loop true)
3. Fires when finding an active customer over 18 with an order over $100
4. Applies a 10% discount to the matching order

• Has a priority of 10 (higher than default)
• Will not re-trigger even if its actions modify objects (no-loop true)
• Fires when finding an active customer over 18 with an order over $100
• Applies a 10% discount to the matching order

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Writing Your First Rule

rule "First-time Customer Discount"
    when
        $customer: Customer(orderCount == 0)
        $order: Order(customer == $customer)
    then
        $order.applyDiscount(15);
        System.out.println("Applied 15% first-time customer discount");
        update($order);
end

1. We have a customer with no previous orders (first-time customer)
2. We have an order associated with this customer

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Additional Resources

• Rule Attributes
• Pattern Matching
• Rule Execution Control