Can't retrieve entity config Error join credit_memo collection

Question

I'm trying to join the collection of refunds and refunds items in this way:

$collection = Mage::getModel('sales/order_creditmemo')->getCollection()
        ->join(array('item'=> 'sales/order_creditmemo_item'),
            'item.parent_id = main_table.entity_id',
            array('sku'=>'item.sku')
        );

But I don't understand why is returning this error:

Fatal error: Uncaught exception 'Mage_Core_Exception' with message 'Can't retrieve entity config: sales/order_creditmemo_item' in /var/www/html/app/Mage.php:603 Stack trace: #0 /var/www/html/app/code/core/Mage/Core/Model/Resource.php(282): Mage::throwException('Can't retrieve ...') #1 /var/www/html/app/code/core/Mage/Core/Model/Resource/Db/Abstract.php(276): Mage_Core_Model_Resource->getTableName('sales/order_cre...') #2 /var/www/html/app/code/core/Mage/Core/Model/Resource/Db/Collection/Abstract.php(488): Mage_Core_Model_Resource_Db_Abstract->getTable('sales/order_cre...') #3 /var/www/html/app/code/core/Mage/Core/Model/Resource/Db/Collection/Abstract.php(569): Mage_Core_Model_Resource_Db_Collection_Abstract->getTable('sales/order_cre...')

After searching for a solution all day long still stuck at this point. Any idea why this behaviour?

Answer 1

I've found the solution about this issue:

$collection = Mage::getModel('sales/order_creditmemo')->getCollection()
        ->join(array('item'=> 'creditmemo_item'),
            'item.parent_id = main_table.entity_id',
            array('sku'=>'item.sku')
        );

I hope will help someone.