last id in codeigniter code example

Example 1: last insert id model codeigniter

function add_post($post_data){
   $this->db->insert('posts', $post_data);
   $insert_id = $this->db->insert_id();

   return  $insert_id;
}

Example 2: codeigniter return last inserted id

$this->db->insert('posts', $post_data);
   $insert_id = $this->db->insert_id();
   return  $insert_id;