I dunno. Help newbe with lib/models please

[eluser]walrus_lt[/eluser]
Hello, i develop website. I am currently creating news/articles and i need your help people. How should i do.

Code:

class Articles_Lib
{
  function get_article($id)
  {
    // articles/article/1484
    if ( is_numeric($id) ){
      return $this->ci->articles_model->get_article_by_id($id);
    // articles/article/some-article-here
    } else {
      return $this->ci->articles_model->get_article_by_uid($id);
    }
  }
}

Vs.

Code:

class Articles_Lib
{
  function get_article($id)
  {
    return $this->ci->articles_model->get_article($id);
  }
}

class Articles_Model extends Model
{
  function get_article($id)
  {
    // articles/article/1484
    if ( is_numeric($id) ){
      return $this->db->query();
    // articles/article/some-article-here
    } else {
      return $this->db->query();
    }
  }
}

I dont want to brake MVC so please help. I would really aprecate your help people.