While Exporting CSV from Sales > Order Grid, I am getting error - "You cannot define a correlation name 'order' more than once"

Question

When I try to export csv in Sales > Order Grid, I am getting

        You cannot define a correlation name 'order' more than once

Trace: #0 /www/Myproject/htdocs/lib/Varien/Db/Select.php(281): Zend_Db_Select->_join('left join', Array, 'order.entity_id...', Array, NULL) #1 /www/Myproject/htdocs/lib/Zend/Db/Select.php(357): Varien_Db_Select->_join('left join', Array, 'order.entity_id...', Array, NULL) #2 /www/Myproject/htdocs/app/code/local/Abc/OrderType/Model/Observer.php(32): Zend_Db_Select->joinLeft(Array, 'order.entity_id...', Array) #3 /www/Myproject/htdocs/app/code/core/Mage/Core/Model/App.php(1339): Abc_OrderType_Model_Observer->salesOrderGridCollectionLoadBefore(Object(Varien_Event_Observer)) #4 /www/Myproject/htdocs/app/code/core/Mage/Core/Model/App.php(1318): Mage_Core_Model_App->_callObserverMethod(Object(Abc_OrderType_Model_Observer), 'salesOrderGridC...', Object(Varien_Event_Observer)) #5 /www/Myproject/htdocs/app/Mage.php(448): Mage_Core_Model_App->dispatchEvent('sales_order_gri...', Array) #6 /www/Myproject/htdocs/app/code/core/Mage/Core/Model/Resource/Db/Collection/Abstract.php(590): Mage::dispatchEvent('sales_order_gri...', Array) #7 /www/Myproject/htdocs/lib/Varien/Data/Collection/Db.php(565): Mage_Core_Model_Resource_Db_Collection_Abstract->_beforeLoad() #8 /www/Myproject/htdocs/app/code/core/Mage/Adminhtml/Block/Widget/Grid.php(951): Varien_Data_Collection_Db->load() #9 /www/Myproject/htdocs/app/code/core/Mage/Adminhtml/Block/Widget/Grid.php(1011): Mage_Adminhtml_Block_Widget_Grid->_exportIterateCollection('_exportCsvItem', Array) #10 /www/Myproject/htdocs/app/code/core/Mage/Adminhtml/controllers/Sales/OrderController.php(703): Mage_Adminhtml_Block_Widget_Grid->getCsvFile() #11 /www/Myproject/htdocs/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Adminhtml_Sales_OrderController->exportCsvAction() #12 /www/Myproject/htdocs/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('exportCsv') #13 /www/Myproject/htdocs/app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http)) #14 /www/Myproject/htdocs/app/code/core/Mage/Core/Model/App.php(354): Mage_Core_Controller_Varien_Front->dispatch() #15 /www/Myproject/htdocs/app/Mage.php(684): Mage_Core_Model_App->run(Array) #16 /www/Myproject/htdocs/index.php(87): Mage::run('', 'store')

And my observer method looks like

public function salesOrderGridCollectionLoadBefore($observer) {
        $collection = $observer->getOrderGridCollection();
        $select = $collection->getSelect();
        $select->joinLeft(array('order' => $collection->getTable('sales/order'))
                , 'order.entity_id=main_table.entity_id'
                , array('type' => 'type'));
    }

Answer 1

It sounds like the event is called multiple times. Causing your code in observer to change the collection multiple times.

You should set a flag on collection and only inject your change if flag is not set. Alternatively determine why event is fired multiple times. Determine if that is correct. Maybe you are using the wrong event for your customization.

Hope that helps.

Answer 2

It's because Magento tries to join the same collection with the same alias twice. Trying using order_new as your alias.