title: How to load catalog model in admin controller
body: <p>I am using Opencart Version 2.1.0.1, how to load frontend model in admin controller,</p>
  
  <p>i have a model function which tells external booking id </p>
  
  <pre><code>class ModelShippingParcelled extends Model {
          public function getParcelledBooking($order_id) {
               $query = $this-&gt;db-&gt;query("SELECT booking_id FROM " . DB_PREFIX . "parcelled WHERE order_id = '" . (int)$order_id . "'");
               return $query-&gt;row;
      }
  </code></pre>
  
  <p>I want to load this model in admin controller. What is the best way to do this?
  Should I rewrite this model in admin too? But I don't want to rewrite the same function. If there is a good way please suggest!</p>