Model query with two possible inputs

[eluser]kirkaracha[/eluser]
I have a list of countries I can access publicly or via a password-protected admin backend. I want to access the countries by URL name from the front end for SEO/usability reasons, and I want to access them by ID on the backend (in case I need to edit the URL name). Here's the query from my model:

Code:

function get_country_info($country_id = null,$country_url_name = null) {
    $this->db->select('
        country_id,
        country_name,
        country_url_name
    ');
    $this->db->from('countries');
    if($country_id != null){
        $this->db->where('country_id',$country_id);
        $this->db->limit('1');
    }
    if($country_url_name != null){
        $this->db->where('country_url_name',$country_url_name);
        $this->db->limit('1');
    }
    return $this->db->get();
} // get_country_info

This works fine if I use ID, but doesn't return any records when I use the URL name. Is there something wrong with my model? How should I do this?

Thanks.