Add & Retrieve Custom Attribute Data from Attribute Set Collection

Question

I need to add additional information for Magento attribute set, like when i add custom attribute for invoice like this:

Mage::app()->setCurrentStore(Mage::getModel('core/store')->load(Mage_Core_Model_App::ADMIN_STORE_ID));
$installer = new Mage_Sales_Model_Mysql4_Setup;

$attribute  = array(
    'type'          => 'datetime',
    'backend_type'  => 'datetime',
    'frontend_input' => 'datetime',
    'is_user_defined' => true,
    'label'         => 'Last Sync',
    'visible'       => true,
    'required'      => false,
    'user_defined'  => false,
    'searchable'    => true,
    'filterable'    => true,
    'comparable'    => true,
    'default'       => NULL
);
$installer->addAttribute('invoice', 'last_sync', $attribute); 

$installer->endSetup();

so i can load the data like this:

$attributeSetCollection = Mage::getResourceModel('eav/entity_attribute_set_collection');
foreach ($attributeSetCollection as $id=>$attributeSet) { 
    $lastSync = $attributeSet->getLastSync();
}

Answer 1

I think you're trying to say that you want to load a custom attribute from an invoice to get it's value. The example you have going on is not what you're looking for, if that's the case.

$invoice = Mage::getModel('sales/invoice')->load( .. );
$invoice->getLastSync(); // this will retrieve the new invoice attribute value for the invoice

If this is not what you're looking for please clarify your question.