Duplicate entities in collection

Question

I'm trying to extend Products in carts report grid. I needed to separate products for each customer and add a Customer name column. So for example a product with id number equal to 123 may exist in two different carts which means for two individual customers. So I need two rows for product id=123.

But at the moment when this happens I get a familiar message:

Item (Mage_Sales_Model_Quote) with the same id "123" already exist

I tried to rewrite my query starting from sales_flat_quote_item as main table (to have unique entities) but since I'm extending Mage_Reports_Model_Resource_Quote_Collection this fails with this error message:

SQLSTATE[42S22]: Column not found: 1054 Unknown column 'main_table.entity_id' 
in 'field list', query was: SELECT STRAIGHT_JOIN COUNT(DISTINCT main_table.entity_id)
FROM `sales_flat_quote_item` AS `main_table` ...

Currently my prepareForProductsInCarts function starts with:

$collection = Mage::getResourceSingleton('sales/quote_item_collection');

and ends with:

// reset methods may be redundant
$this->getSelect()
    ->useStraightJoin(true)
    ->reset(Zend_Db_Select::COLUMNS)
    ->reset(Zend_Db_Select::DISTINCT)
    ->reset(Zend_Db_Select::GROUP)
    ->reset(Zend_Db_Select::WHERE);
$this->getSelect()->setPart(Zend_Db_Select::COLUMNS, $collection->getSelect()->getPart(Zend_Db_Select::COLUMNS));
$this->getSelect()->setPart(Zend_Db_Select::FROM, $collection->getSelect()->getPart(Zend_Db_Select::FROM));
$this->getSelect()->setPart(Zend_Db_Select::GROUP, $collection->getSelect()->getPart(Zend_Db_Select::GROUP));
$this->getSelect()->setPart(Zend_Db_Select::WHERE, $collection->getSelect()->getPart(Zend_Db_Select::WHERE));

What can I do to allow or work around duplicated entities?

Answer 1

I was extending Mage_Reports_Model_Resource_Quote_Collection:

class Name_Sapce_Model_Resource_Reports_Quote_Collection
    extends Mage_Reports_Model_Resource_Quote_Collection {

and after going through base codes I found the only thing I need to change to set my own resource model is invoking _init() from _construct method this way:

protected function _construct()
{
    Mage_Core_Model_Resource_Db_Collection_Abstract::_construct();
    $this->_init('sales/quote_item');
}

An escape to call parent::_construct(); may be necessary and that's the reason why I used parent's parent class directly.

Now main_table correctly is an alias for sales_flat_quote_item.