Codeigniter thumbnail image path can not be stored in MySql

I am trying to make a simple app with Codeigniter where i need to store thumbnail image path in MySql database. The images along with the thumbnail versions upload correctly in the upload folder and I can store the image path in my database while uploading but i can not store the thumbnail image path in the database. I tried this in the controller:

$thumbnail= $this->resize($data['upload_data']['full_path'], $data['upload_data']  ['file_name']);
$thumbnail_path = './uploads/'. $thumbnail;
$newRow = array(
                    "title" => $this->input->post('title'),
                    "img_path" => $imgpath,
                    "thumbnail_path" => $thumbnail_path,
                    "post_body" => $this->input->post('post_body')
                    )

But it only stores "./uploads/" in the thumbnail_path column in my table, not the actual thumbnail path. Where i expect it to store something like "./uploads/Lighthouse_thumb.jpg". I can not figure out how to get the path of the thumbnail images to store them in the database. Here is my full upload controller:

  class Upload extends CI_Controller
  {

function __construct()
{
    parent::__construct();
    $this->load->helper('form');    
}
function index() {

        $this->load->view('upload_form', array('error'=>''));
    }

function do_upload() {
    $config['upload_path'] = './uploads/';
    $config['allowed_types'] = 'gif|jpg|png';
    $config['max_size'] = '1000';
    $config['max_width']  = '1024';
    $config['max_height']  = '768';

    $this->load->library('upload', $config);

    if (!$this->upload->do_upload()) {
        $error = array('error' => $this->upload->display_errors());
        $this->load->view('upload_form', $error);
    } else {
        $image_data = $this->upload->data();
        $imgpath = './uploads/' . $image_data['file_name'];
        $data = array('upload_data'=>$this->upload->data());
        $thumbnail= $this->resize($data['upload_data']['full_path'], $data['upload_data']['file_name']);
        $thumbnail_path = './uploads/'. $thumbnail;
        $newRow = array(
                    "title" => $this->input->post('title'),
                    "img_path" => $imgpath,
                    "thumbnail_path" => $thumbnail_path,
                    "post_body" => $this->input->post('post_body')
                    );
            $this->load->model('postimage_path');
            $this->postimage_path->insert($newRow);
            $this->load->view('upload_success', $data);
    }

    }
function resize($path, $file) {
        $config['image_library'] = 'gd2';
        $config['source_image'] =  $path;
        $config['create_thumb'] = TRUE;
        $config['maintian_ratio'] = TRUE;
        $config['width'] = 100;
        $config['height'] = 100;
        $config['new_image'] = './uploads/' . $file;

        $this->load->library('image_lib', $config);
        $this->image_lib->resize();

    }

}

$thumbnail_path = './uploads/'. $thumbnail;

So thumbnail_path contains only "./uploads/" : that tells us that $thumbnail is false (or null or empty string etc.), meaning that the return value of the call to resize is wrong - it seems you expect it to return the file name.

function resize($path, $file) {
    $config['image_library'] = 'gd2';
    $config['source_image'] =  $path;
    $config['create_thumb'] = TRUE;
    $config['maintian_ratio'] = TRUE;
    $config['width'] = 100;
    $config['height'] = 100;
    $config['new_image'] = './uploads/' . $file;

    $this->load->library('image_lib', $config);
    $this->image_lib->resize();

}

resize returns nothing! And you assign that nothing to $thumbnail_path. That's your problem.

You seem to have simply copied the code from the CodeIgniter docs. From said docs (emphasis mine):

The above code tells the image_resize function to look for an image called mypic.jpg located in the source_image folder, then create a thumbnail that is 75 X 50 pixels using the GD2 image_library. Since the maintain_ratio option is enabled, the thumb will be as close to the target width and height as possible while preserving the original aspect ratio. The thumbnail will be called mypic_thumb.jpg

So there you have it! If your filename is $data['upload_data']['file_name'], your thumbnail will be $data['upload_data']['file_name'] . "_thumb". Have a look at your file system, the files should be there for you to see.

So to fix your problem, this should do the trick:

 $pathinfo = pathinfo($data['upload_data']['file_name']);
 $thumbnail_path = './uploads/'. $data['upload_data']['file_name'] . "_thumb" . $pathinfo['extension'];