Example

<?php

class Example extends CI_Controller {

    public function __construct() {
        parent::__construct();
        $this->load->model('ExampleModel');
    }

    public function index() {
        $data['records'] = $this->ExampleModel->findAll();
        $this->load->view('example/index', $data);
    }

    public function create() {
        $this->_save(false);
        $data['records'] = [];
        $this->load->view('example/form', $data);
    }

    public function update() {
        $id = $this->uri->rsegnemt(n);
        if (!$id) {
            show_404();
        }
        $records = $this->ExampleModel->findBy($id);
        if (!$records) {
            show_404();
        }
        $this->_save($id);
        $data['records'] = $records;
        $this->load->view('example/form', $data);
    }

    public function _save($id = false) {
        $post = $this->input->post();
        if ($post && $this->ExampleModel->validate($post)) {
            $data = $this->ExampleModel->prepareData($post);
            $insertId = $this->ExampleModel->save($data, $id);
            redirect('example/update/' . $insertId);
        }
    }

}

class ExampleModel extends CI_Model {

    public function __construct() {
        parent::__construct();
    }

    public function validate($post) {

    }

    public function prepareData($post) {

    }

    public function save($data, $id = false) {
        if (!$id) {
            $this->db->insert('table', $data);
            return $this->db->insert_id();
        }
        $this->db->update('table', $data, ['id' => $id]);
        return $id;
    }

}