SELECT incident.*, COUNT(comment.id) AS com 
FROM incident 
LEFT JOIN comment ON comment.incident_id=incident.id 
GROUP BY incident.id 
ORDER BY com DESC

$content->incidents = ORM::factory('incident')
         ->with('location')
         ->join('incident_category', 'incident.id', 'incident_category.incident_id')
         ->where('incident_active', '1')
         ->where('category_id', $category_id)
         ->limit('10')
         ->orderby('incident_date', 'desc')
         ->find_all();

SELECT incident.*
  FROM incident
  JOIN (
    SELECT count(comment.id) AS c, comment.incident_id 
      FROM comment
      GROUP BY comment.incident_id 
    ) com
    ON com.incident_id=incident.id
  ORDER BY com.c DESC

  
$query = DB::query(Database::SELECT, 'здесь запрос');
$result = $query->as_object('Model_Incident')->execute();             

Fatal error: Class 'DB' not found in /var/www/ushahidi/themes/112_cloud/hooks/register_commented_blocks.php on line 37