Model class inheriting from Base_model class. See Medium article for details:

post_child.php

<?php if(!defined('EXT')) exit("Invalid file request");

/**
* Post Model Class
*
* @package     ci_model_example
* @author      Patrick Pohler [email protected]
* @copyright   Copyright (c) 2014, Patrick Pohler
* @link        http://www.anecka.com/rets_press
* @license		 MIT
*/

require PATH_THIRD."ci_model_example/models/base_model.php";

class Post_child extends Base_model {
    var $title = '';
    var $name = '';
    var $date = null;
    var $author_secret = '';

    function __construct() {
        ee()->load->library('encrypt');

        parent::__construct();
    }

    protected function _set_model_for_save($data) {
        $this->site_id = $data['site_id'];
        $this->title = $data['title'];
        $this->name  = $data['name'];
        $this->date = $data['date'];
        $this->author_secret = ee()->encrypt->encode($data['author_secret']);
    }

    protected function _set_model_for_return($row) {
        $this->id = $row->id;
        $this->site_id = $row->site_id;
        $this->title = $row->title;
        $this->name = $row->name;
        $this->date = $row->date;
        $this->author_secret = ee()->encrypt->decode($row->author_secret);
    }
    
    protected function _get_table(){
        return "posts";
    }
}