binding an array to multiple text fields in a form

I have a model that has the following classes: ShoppingList, Item and

-- *Product* is just a list of product names: Apple, Orange, Banana,
Grape. The table has two columns: ID and NAME.

-- A *ShoppingList* has a name (string) and many *Item* objects.

-- Each *Item* has a *quantity* (integer) and to-one relationship to

My ShoppingList's edit view has a form that contains a textfield for
the name of
a shopping list and a table of items and their quantities:

Name: MyShoppingList

Qty. Item
3 Apples
0 Oranges
1 Pear

The Qty. is an editable text field. The Item is a non-editable text

The model object for this view is, of course, a ShoppingList.

I am trying to bind each text field to the quantity attribute of each
item in the shopping list. I tried something like this but it doesn't
work because Rails wants an instance variable to bind to. How do I
properly bind my array?

<% @shopping_list.items.each do |item| %>
<td><%= text_field("shopping_list.items[" + +
item.quantity, :size => 3) %></td><td><%= (Product.find
<% end %>

Let me try to simplify this problem:

To create the html table, I have this code:

<% @shopping_list.items.each do |item| %>
<td><%= text_field("item.quantity", item.quantity, :size => 3) %></

<td><%= (Product.find item.product_name_id).name%></td>

<% end %>

But it generates this error:

`@item.quantity' is not allowed as an instance variable name

This tells me that you can only bind instance variables and not
relationships off them. Is this true? Where can I find a detailed
explanation on how binding forms to variables work?

Never mind. I figured it out. The solution is to use the fields_for
tag. The problem was editing multiple models in one large form.