Adding Dummy Column in Kohana ORM

I want to add dummy column in kohana ORM . I have a field of type longtext . I want to have开发者_开发技巧 a new field which contains it's strlen.

Use $_ignored_columns property:

protected $_ignored_columns = array('text_length');

public function __get($column)
{
   if ($column == 'text_length' && (! isset($this->_object['text_length']) || isset($this->_changed['text'])))
   {
      // recalc dummy field if not set, or on long text value changing
      return $this->_object['text_length'] = strlen($this->_object['text']);
   }

   return parent::__get($column);
}