根据CodeIgniter中的另一个更改下拉列表

Question

我是CI的新手。我需要根据另一个下拉列表更改一些下拉列表。

我的控制器代码：

public function index()
{
    $data = array();
    $data['from_list']          =  $this->from->list_from();
    $data['to_list']            =  $this->to->list_to();
    $data['fromwhere_list']         =  $this->fromwhere->list_fromwhere();
    //$data['fromwhere_from_list']          =  $this->fromwhere->list_fromwhere_from();
    $data['towhere_list']           =  $this->towhere->list_towhere();
    $data['header']         =  array('view'=>'header','data'=>array());
    $data['main_content']   =  array('view'=>'home','data'=>array());
    $data['footer']         =  array('view'=>'','data'=>array());

    $this->load->view('template',$data);

    //$this->load->view('home');
}

模型代码

function list_fromwhere()
{
    $this->db->select('fromwhere_id,from_id,from_from_name');
    $this->db->from('mt_from_from');        
    $query = $this->db->get();
    return $query->result();        
}
function list_from()
{
    $this->db->select('from_id,from_name');
    $this->db->from('mt_from');     
    $query = $this->db->get();
    return $query->result();        
}

我的观看代码

<select class="" name="from" id="from" style="width: 20%;-webkit-border-radius: 3px;-moz-border-radius: 3px;border-radius: 3px;border: none;background: #dfe7eb;color: #999999;height: 38px;line-height: 38px;padding-left: 10px;padding-right: 20px;">
                        <?php

                        foreach($from_list as $from_item)
                        {
                        ?>
                        <option value="<?php echo $from_item->from_id?>"><?php echo $from_item->from_name?></option>
                        <?php   
                        }

                        ?>

                        <!-- <option value="volvo">Airport</option>
                        <option value="saab">Town</option>
                        <option value="mercedes">Hotel</option> -->
                    </select>

                    <select class="" name="from_place" id="from_place"  style="width: 56%;-webkit-border-radius: 3px;-moz-border-radius: 3px;border-radius: 3px;border: none;background: #dfe7eb;color: #999999;height: 38px;line-height: 38px;padding-left: 10px;padding-right: 20px;">

                    <?php
                        foreach($from_list as $from_item){
                        foreach($fromwhere_list as $fromwhere_item)
                        {
                            if($fromwhere_item->from_id == $from_item->from_id){
                        ?>
                        <option value="<?php echo $fromwhere_item->fromwhere_id?>"><?php echo $fromwhere_item->from_from_name?></option>
                        <?php
                            }
                        }   
                        }

                        ?>
                    </select>

当我们从下拉列表（firstone）中选择城镇，国家时，我需要自动从地点下拉列表（secondone）更改。