src/Cart/OrderTotalCalculator.php
public function getModifier($className, $forcecreate = false)
    {
        if (!ClassInfo::exists($className)) {
            user_error("Modifier class \"$className\" does not exist.");
        }
        //search for existing
        $modifier = $className::get()
            ->filter("OrderID", $this->order->ID)
            ->first();
        if ($modifier) {
            //remove if no longer valid
            if (!$modifier->valid()) {
                //TODO: need to provide feedback message - why modifier was removed
                $modifier->delete();
                $modifier->destroy();
                return null;
            }
            return $modifier;
        }
        $modifier = new $className();
        if ($modifier->required() || $forcecreate) { //create any modifiers that are required for every order
            $modifier->OrderID = $this->order->ID;
            $modifier->write();
            $this->order->Modifiers()->add($modifier);

            return $modifier;
        }

        return null;
    }
public function getModifier($className, $forcecreate = false)
    {
        if (!ClassInfo::exists($className)) {
            user_error("Modifier class \"$className\" does not exist.");
        }
        //search for existing
        $modifier = $className::get()
            ->filter("OrderID", $this->order->ID)
            ->first();
        if ($modifier) {
            //remove if no longer valid
            if (!$modifier->valid()) {
                //TODO: need to provide feedback message - why modifier was removed
                $modifier->delete();
                $modifier->destroy();
                return null;
            }
            return $modifier;
        }
        $modifier = new $className();
        if ($modifier->required() || $forcecreate) { //create any modifiers that are required for every order
            $modifier->OrderID = $this->order->ID;
            $modifier->write();
            $this->order->Modifiers()->add($modifier);

            return $modifier;
        }

        return null;
    }
Retrieve a modifier of a given class for the order.
Modifier will be retrieved from database if it already exists,
or created if it is always required.

@param string  $className
@param boolean $forcecreate - force the modifier to be created.