Magento – How to get collection from table ‘sales_flat_creditmemo_item’

Actually getAllIds is the best way of doing it. For example in the product collection resource model the method looks like this:

public function getAllIds($limit = null, $offset = null)
{
    $idsSelect = $this->_getClearSelect();
    $idsSelect->columns('e.' . $this->getEntity()->getIdFieldName());
    $idsSelect->limit($limit, $offset);
    $idsSelect->resetJoinLeft();

    return $this->getConnection()->fetchCol($idsSelect, $this->_bindParams);
}

So everything is retrieved from a single select and no iteration is required. Also in the abstract resource model it looks like this:

public function getAllIds()
{
    $idsSelect = clone $this->getSelect();
    $idsSelect->reset(Zend_Db_Select::ORDER);
    $idsSelect->reset(Zend_Db_Select::LIMIT_COUNT);
    $idsSelect->reset(Zend_Db_Select::LIMIT_OFFSET);
    $idsSelect->reset(Zend_Db_Select::COLUMNS);

    $idsSelect->columns($this->getResource()->getIdFieldName(), 'main_table');
    return $this->getConnection()->fetchCol($idsSelect);
}

So everything that extends Mage_Core_Model_Resource_Db_Collection_Abstract should use this unless specified otherwise.

The method you looked at comes from the base class Varien_Data_Collection but it is overwritten in its children.

http://www.magentocommerce.com/knowledge-base/entry/magento-for-dev-part-7-advanced-orm-entity-attribute-value

$installer->createEntityTables(
    $this->getTable('complexworld/eavblogpost')
);

The article is really long...

If the tables exist, you can use a collection extended from EAV collection

class Magentotutorial_Complexworld_Model_Resource_Eavblogpost_Collection extends Mage_Eav_Model_Entity_Collection_Abstract
{
    protected function _construct()
    {
        $this->_init('complexworld/eavblogpost');
    }
}