Difference between saving methods

Question

I’m currently using the following code to update/save invoices & orders after creating a partial invoice.

$invoice->getOrder()->setIsInProcess(true);
Mage::getModel('core/resource_transaction')
    ->addObject($invoice)
    ->addObject($invoice->getOrder())
;
$invoice->save();
$order->save();

To me, it looks like both $invoice->save() & the adding an object to the resource transaction do the same thing.

Should I still be using both, or should I only use one or the other?

Answer 1

You should use it like this:

$invoice->getOrder()->setIsInProcess(true);
Mage::getModel('core/resource_transaction')
    ->addObject($invoice)
    ->addObject($invoice->getOrder())
    ->save()
;

It is somehow similar with

$invoice->save();
$order->save();

The only difference is that both saves are done inside a single transaction. So if something goes wrong when saving the order, the invoice will be rolled back also. If you call them separately there is a chance that the invoice save will work and the order save won't. In this case only the order will be rolled back. This leads to inconsistent data in your db.