public function setRequired($keys)
    {
        if(is_string($keys))
        {
            $this->setRequired(explode(",",$keys));
        }
        else
        {
            foreach($keys as $key)
            {
                if(!in_array($key, $this->required))
                    $this->required[] = $key;
            }
        }

        return $this;
    }