Models, where, when and why?

Okay, that goes back to complicating things.

Libraries should not have access to database. Fair enough, that means what I use as library should be a model. Then, back to the situation with the blog post. I have a post with various details. One of them being a category, the other an author. But, as these categories and authors have various details too, they're their own objects.

So when I want to display the post-content, I just do echo $post->content; and be done with it. When I want to display the posts authors name, this would be echo $post->author->name;.

Now I do this by using libraries. But, as said, I'm probably using libraries where I should be using models. My setup would then be something like this?

Code:

class Post_model extends CI_Model {
    public $id;
    public $title;
    public $content;
    public $category;
    public $author;

    public function get_data($postID) {

        // Get the required Post
        $result = $this->db->where('id', $postID)->get('posts');

        // If result of query is 1 (should be only one post with that ID)
        if($result->num_rows == 1) {

            // Store the resulting row as... Object?
            $post = $result->row(0, 'Post_model');

            // And then comes the fun part. Create an empty Author,
            // Call its get_data function and store the resulting object as
            // this posts author
            $author = new Author;
            $post->author = $author->get_data($post->author);

            // And the same goes for the category
            $category = new Category;
            $post->category=  $category->get_data($post->category);

            // All done? Then return this model
            return $post;

        }
    }
}

Code:

class Category_model extends CI_Mode {
    public $id;
    public $name;
    public $parent;

    public function get_data($categoryID) {

        // Get the required Category
        $result = $this->db->where('id', $categoryID)->get('categories');

        // If result of query is 1 (should be only one category with that ID)
        if($result->num_rows == 1) {    

            // return the category as an object
            return $result->row(0, 'Category_model');
        }    
    }
}

// and the same for the user

So once I've done that, I can call my controller like http://domain.com/blog/post/15, so my controller has the following method::

Code:

public function post($postID) {

    // Create a new Post object
    $post = new Post;

    // Fill the object with data from id $postID (method-call)
    $data['post'] = $post->get_data($postID);

    // And send it to the view
    $this->load->view('blogpost', $data);
}

Lean controller, fat model. Right?

I'm thinking I've been doing something terribly wrong all along...