CodeIgniter Update Not Working - codeigniter

Question

I have a form in a modal that I'm using to do an update on a record. The form seems to submit okay, the URL in the browser points to the right location (domain.net/cities/update_city/1) but no view shows up and the record is never updated. I've searched the internet but most tutorials seem to skim over the update or hardcode the id to update. I've only been using CI for a week.
Model Code
// Edit City
function edit_city($city_id) {
$data = array('city_name' => $this->input->post('city_name'));
$this->db->where('city_id', $city_id);
$this->db->update('cities', $data);
}
View Code (Form is in a modal and gets city_id added by jQuery)
<div class="modal-body">
<?php $this->load->helper('form'); ?>
<?php echo form_open('/cities/update_city/'); ?>
<label class="control-label" for="name">City</label>
<input type="text" name="city_name" id="city_name" value=""/><br />
<input type="submit" name="submit" class="btn-small btn-primary" value="Edit City" />
<button class="btn-small" data-dismiss="modal">Cancel</button>
<?php echo form_close(); ?>
</div>
<script>
// scripts for modal windows
$(document).on("click", ".edit-modal", function () {
var city_name = $(this).data('name');
var city_id = $(this).data('id');
$(".modal-body #city_name").val( city_name );
//set the forms action to include the city_id
$(".modal-body form").attr('action','/cities/update_city/'+city_id);
$('#editCityDialog').modal('show');
});
Controller Code
// Update City
function update_city($city_id) {
$this->load->model('cities_model');
if ($this->input->post('submit')) {
$data = array('city_name' => $this->input->post('city_name'));
$this->cities_model->edit_city('cities', array('city_id' => $city_id),$data);
redirect('/cities');
}
}

Answer 1

Here is an example, you can use it to update easily (i'm bad at english, sorry).
Model:
class Cities_model extends CI_Model{
function edit($table,$where,$data){
foreach ($where as $key => $value){
$this->db->where($key,$value);
}
$this->db->update($table,$data);
}
}
Controller:
function update_city($city_id){
$this->load->model('cities_model');
if($this->input->post('submit'){
$data = array('city_name' => $this->input->post('city_name'));
$this->cities_model->edit('cities',array('city_id' => $city_id),$data); //(table,where,data); see in model.
redirect('');
}
}
* if you go a link as "http://......update_city/2" and a function update_city($city_id), $city_id will receive as "2" and you need not to write uri_segment to get $city_id. Hope that help you
EDIT :
Controller:
function update_city($city_id) {
$this->load->model('cities_model');
if ($this->input->post('submit')) {
$this->cities_model->edit_city($city_id);
redirect('/cities');
}
}