CakePHP edit multiple records at once

I have a HABTM relationship between two tables: items and locations, using the table items_locations to join them.

items_locations also stores a bit more information. Here's the schema

items_locations(id, location_id, item_id, quantity)

I'm trying to build a page which shows all the items in one location and lets the user, through a datagrid style interface, edit multiple fields at once:

Location: Factory XYZ
 ___________________________
|___Item____|___Quantity___|
| Widget    |          3   |
| Sprocket  |          1   |
| Doohickey |         15   |
----------------------------

To help with this, I have a controller called InventoryController which has:

var $uses = array('Item', 'Location');  // should I add 'ItemsLocation' ?

How do I build a multidimensional form to edit this data?


Edit:

I'm trying to get my data to look like how Deceze described it below but I'm having problems again...

// inventory_controller.php
function edit($locationId) {

    $this->data = $this->Item->ItemsLocation->find(
        'all',
        array(
            "conditions" => array("location_id" => $locationId)
        )
    );

when I do that, $this->data comes out like this:

Array (
    [0] => Array (
        [ItemsLocation] => Array (
            [id] => 16
            [location_id] => 1
            [item_id] => 1
            [quantity] => 5
        )
    )
    [1] => Array (
        [ItemsLocation] => Array (/* .. etc .. */)
    )
)