Convert query with subquery in SELECT clause to CodeIgniter's query builder

$query = $this->db->query(
    'SELECT g.gallery_id, g.gallery_title, (
         SELECT i.gallery_image_path
         FROM nepal_gallery_image AS i
         WHERE i.gallery_id = g.gallery_id
         AND i.gallery_image_status =  "Enabled"
         LIMIT 0 , 1) AS gallery_image_path
     FROM nepal_gallery AS g
     WHERE g.gallery_status =  "Enabled"'
);

The above query gives the correct output.

However, when I use the CI subquery library:

$this->load->library('Subquery');
$this->db->select('g.gallery_id,g.gallery_title');
$sub = $this->subquery->start_subquery('select');
$sub ->select('i.gallery_image_path')
     ->from('nepal_gallery_image AS i')                 
     ->where(array('i.gallery_image_status'=>"Enabled",  
                   'i.gallery_id'=>"g.gallery_id")) 
     ->limit(0,1);
$this->subquery->end_subquery('gallery_image_path'); 
$this->db->from('nepal_gallery AS g');
$this->db->where('g.gallery_stats',"Enabled");
$query=$this->db->get();

the resulting query is:

SELECT `g`.`gallery_id` , `g`.`gallery_title` , (
  SELECT `i`.`gallery_image_path`
  FROM (`nepal_gallery_image` AS i)
  WHERE `i`.`gallery_image_status` = 'Enabled'
  AND `i`.`gallery_id` = 'g.gallery_id'
  LIMIT 0 , 1 ) AS gallery_image_path
FROM (`nepal_gallery` AS g)
WHERE `g`.`gallery_status` = 'Enabled'

and the output is not as expected.

the output in first query is

    <table>
     <tr>
         <th> gallery_id</th>
         <th> gallery_title</th>
         <th> gallery_image_path </th>
     </tr>
     <tr>
        <td>1</td>
        <td>Gallery 1</td>
        <td>images/image1.jpg</td>
     </tr>
     <tr>
        <td>2</td>
        <td>Gallery 2</td>
        <td>images/image2.jpg</td>
     </tr>
     </table>

However, in later query, the output is

    <table>
     <tr>
         <th> gallery_id</th>
         <th> gallery_title</th>
         <th> gallery_image_path </th>
     </tr>
     <tr>
        <td>1</td>
        <td>Gallery 1</td>
        <td>NULL</td>
     </tr>
     <tr>
        <td>2</td>
        <td>Gallery 2</td>
        <td>NULL</td>
     </tr>
     </table>

It seems the problem is with the subquery.

the problem is that the subqueries where condition is taking your table alias g as string 'g.gallery_id' one way to avoid the CI's protect fields is by passing third parameter as false in where condition so CI will not try to protect your field or table names with backticks.

try this

 $sub ->select('i.gallery_image_path')
 ->from('nepal_gallery_image AS i')                 
 ->where(array('i.gallery_image_status'=>"Enabled",  
               'i.gallery_id'=>"g.gallery_id"), NULL, FALSE);
                                           //--^^^^^^^^^^^^^^--here 
 ->limit(0,1);

or the simply write your clauses manaully

  $where = "i.gallery_id = g.gallery_id AND i.gallery_image_status =  'Enabled'";
  $sub ->select('i.gallery_image_path')
 ->from('nepal_gallery_image AS i')                 
 ->where($where,NULL,FALSE); 
 ->limit(0,1);