I have followed the guide here by Volodymyr Vygovskyi, everything is working well, apart from when you filter by a sku, it causes the issue:
Strict Notice: call_user_func() expects parameter 1 to be a valid callback, non-static method Atwix_ExtendedGrid_Model_Observer::filterSkus() should not be called statically in /Applications/XAMPP/xamppfiles/htdocs/mag19/app/code/core/Mage/Adminhtml/Block/Widget/Grid.php on line 468
Investigating this I can see that he has the following as his filter_condition_callback:
'filter_condition_callback' => array('Atwix_ExtendedGrid_Model_Observer', 'filterSkus'),
whereby the observer is being called statically here:
'Atwix_ExtendedGrid_Model_Observer'
In my attempts to fix this, I changed this to the variable $this, which causes the filterSkus function to not be found.
Thus, I then attempted to move the filter function to the helper data.php file. This then led to the sku column in sales_flat_order_item to not be found.
Likewise also tried changing the string declaration of the observer to Mage::getSingleton('Atwix_ExtendedGrid_model_observer'). But, this then causes the following error:
SQLSTATE[42S22]: Column not found: 1054 Unknown column 'sales_flat_order_item.sku' in 'where clause', query was: SELECT COUNT(DISTINCT main_table.entity_id) FROM `sales_flat_order_grid` AS `main_table` WHERE ((sales_flat_order_item.sku like '%lab%'))
I am at a loggerhead with how to fix this issue, thus was hoping someone could help me.