in the model

gistfile1.php

<?php

  function save($id=null)
  {
    $this->title = $this->input->post('title');
    $this->code = $this->input->post('code');
    $this->permalink = $this->input->post('permalink');

    if ($this->input->post("id")){ // is there an id
      $this->modified = date('Y-m-d H:i:s'); // then it's modified
      $this->db->update('pages',$this, array('id'=>$this->input->post('id')));
    } else {
      $this->created = date('Y-m-d H:i:s'); // then it's created
      $this->modifed = $this->created;
      $this->db->insert('pages',$this);
    }
  }