Let me start with some context. I'm operating in Magento Enterprise Edition 1.8.0.0 and I am relatively new to Magento Development.
I have seen questions similar to this on Stack Overflow, forums, and blogs, but the answer tends to be something like the one I came up with myself:
$parentIds = (Mage::getModel('catalog/product_type_grouped')->getParentIdsByChild($_item->getProductId());
$parentId = $parentIds[0];
It's true that this will retrieve a Parent ID, but it will not always retrieve the right one. The "right" Parent ID, in my case, is the one belonging to the Grouped Product from which a Simple Product was placed in the cart and eventually ordered.
The file I'm trying to get this logic into is:
my_template_path/email/order/items/order/default.phtml
The end goal is to retrieve the thumbnail image of the right Grouped Product in an Order Confirmation Transactional Email. Any ideas?