我想在模型上添加新字段，但是我做不到。谁能帮我吗？
这是我在模型上的功能
public function get_item(){
$default_language = setting_value('default_language');
$query = $this->db->order_by('p.id','desc')
->select("p.* , c.name as item_name, a.name as category_name")
->join("content_to_" . $this->url ." c", "c.item_id = p.id" , "left")
->join("content_to_item_category a", "p.item_category_id = a.item_category_id" , "left")
->get_where($this->url ." p",array('c.language_id'=> $default_language,'a.language_id'=> $default_language, 'p.flag !=' => 3))->result_array();
return $query;
}