Getting array parameters from POST

[eluser]derekt[/eluser]
I'm writing a page to reorder images using JQuery and Ajax to POST the image order back to my controller so I can update the database; I've got the page returning this via POST:

POST
item[] 17
item[] 1
item[] 9

However, the database isn't updating. I'd really appreciate some advice on what I'm missing here. The controller function looks like this:

Code:

function index ()
    {
        foreach($this->input->post('item',TRUE) as $key=>$value):
        {
                $this->db->where('id', $value)->update('photo_order_map', array ('sort_order'=>$key));
        }
    }

I tried setting $config['enable_query_strings'] = TRUE; to no avail.
Any suggestions??

Thanks!