<?php

class Orange35_CustomInvoicesGenerator_Model_Resource_Order_Collection extends Mage_Core_Model_Resource_Db_Collection_Abstract
{
    protected function _construct()
    {
        $this->_init('orange35_custominvoicesgenerator/order');
    }

    public function  getPaymentSumAndCount()
    {
        $paymentsTable = Mage::getResourceModel('orange35_custominvoicesgenerator/invoice')->getMainTable();
        $paymentStatus = Mage_Paypal_Model_Info::PAYMENTSTATUS_COMPLETED;
        $this->getSelect()->columns(
            array(
                'paid_sum'       => new Zend_Db_Expr("(SELECT sum(paid) FROM " . $paymentsTable
                        . " WHERE order_id=main_table.id AND payment_status='" . $paymentStatus . "')"),

                'payments_count' => new Zend_Db_Expr("(SELECT COUNT(*) FROM " . $paymentsTable
                        . " WHERE order_id=main_table.id AND payment_status='" . $paymentStatus . "')"),
            ));
        return $this;
    }

}