Magento Tips: Magento Fatal error: Call to a member function extend() on a non-object

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If you get this error:

Fatal error: Call to a member function extend() on a non-object in /public_html/app/code/core/Mage/Core/Model/Mysql4/Config.php on line 115

After MySQL dump import in a Magento database, most likely Magento MySQL tables had wrong values in some fields.

This happens when default auto_value_for_zero option is activated in MySql.

To fix the error add these commands in the beginning of a MySQL dump you want to import:

[cc lang='sql' ]
SET FOREIGN_KEY_CHECKS=0;
SET SQL_MODE="NO_AUTO_VALUE_ON_ZERO";

Most likely it will fix the Magento fatal error.

If the database is already imported, you can fix the issue using these MySQL commands:

[cc lang='sql' ]
UPDATE 'core_website' SET 'website_id' = 0 WHERE 'code' like 'admin';
UPDATE 'core_store' SET 'store_id' = 0 WHERE 'code' like 'admin';
UPDATE 'customer_group' SET 'customer_group_id' = 0 WHERE 'customer_group_code' like 'NOT LOGGED IN';

These commands will reset the website_id, store_id and customer_group_id values to zero for admin user and 'not logged in' user type.