Observer not working sales_order_invoice_save_after

Question

This function not working because what i'm trying to achieve is if this invoice contain a product with sku "FBA" then assign this status.

Looking forward to hearing from you.

But it doesn't work as i'm getting this:

exception 'Varien_Exception' with message 'Invalid method Mage_Sales_Model_Order_Invoice::addStatusHistoryComment(Array
(
    [0] => Amazon FBA
    [1] => amazonfba
)

public function changestatus2($event)
{
    $_order = $event->getEvent()->getInvoice();
    $_state = 'amazonfba';

    foreach($_order->getAllItems() as $item) {
        $sku = $item->getSku();
        if (substr($sku,-4) == '_FBA') {
        $_order->addStatusHistoryComment('Amazon FBA', $_state)
            ->setIsVisibleOnFront(false)
            ->setIsCustomerNotified(false)
            ->save();
            break;
        }
    }
}

Answer 1

Problem 1: addStatusHistoryComment belongs to Mage_Sales_Model_Order and not to Mage_Sales_Model_Order_Invoice, so you'll get this error.

Problem 2: if you want to alter order status, you have to do this also in Mage_Sales_Model_Order

If it doesn't matter you can set your comment to the order, instead of the invoice, changig observer to sales_order_save_before.

Problem 3: sales_order_save_before is triggered twice, what results in duplicated comments.

So i came up with following solution ...

public function changestatus2(Varien_Event_Observer $observer)
{
    $order = $observer->getOrder();
    $status = 'amazonfba';

    if (!$order->getFbaFlag()) {
        foreach ($order->getAllItems() as $item) {
            if (substr($item->getSku(), -4) == '_FBA') {
                $order->addStatusHistoryComment('Amazon FBA', $status);
                break;
            }
        }
    }

    $order->setStatus($status); // set status for 2nd fired event
    $order->setFbaFlag(true); // set pseudo-flag, so that comment is only added one time
}

This adds your comment once and finally set your order status to amazonfba.

Answer 2

This is wrong

$_order = $event->getEvent()->getInvoice();

Need to be

$_order = $event->getEvent()->getInvoice()->getOrder();

Change it and will work.