I've found editing AdminCategoriesController.php can add custom form fields to Backoffice, but when I save the form I get error updating category() object
I have already added the field to database table and Category.php
class CategoryCore extends ObjectModel
{
public $myfield;
...
public static $definition = array(
'table' => 'category',
'primary' => 'id_category',
'multilang' => true,
'multilang_shop' => true,
'fields' => array(
...
'myfield' => array('type' => self::TYPE_HTML, 'lang' => true, 'validate' => 'isCleanHtml'),
),
);
...
}