Invoice ID Column Null in Credit Memo Table

Question

Has anybody else noticed that the invoice_id column in sales_flat_creditmemo is always Null?

The order_id column is populated, but nothing in the invoice_id column. Is this just me?

Answer 1

So, I had a quick grep, and in app/code/core/Mage/Adminhtml/Block/Sales/Order/Creditmemo/Create.php there's this function

public function getHeaderText()
{
   if ($this->getCreditmemo()->getInvoice()) {
       $header = Mage::helper('sales')->__('New Credit Memo for Invoice #%s', $this->getCreditmemo()->getInvoice()->getIncrementId());
   }
   else {
       $header = Mage::helper('sales')->__('New Credit Memo for Order #%s', $this->getCreditmemo()->getOrder()->getRealOrderId());
   }
   return $header;
}

This reminded me that there's at least two places you can create a credit memo from, depending on your payment provider.

We use Ebizmarts_Sagepay for most of our orders, and we can create a credit memo from the order, and we can also create a credit memo from the invoice. If we do it from the invoice we'll get the header that says for Invoice #%s, if we do it from the order we'll get the header that says for Order #%s.

We also use M2E_Pro and on those order we do a credit memo on the invoice. So I'd guess it depends on whether the payment methods supports refunds.