Dynamic Partial Based on Select Box - Rails 2.3.5 - ruby-on-rails

Question

I've edited my request to hopefully be clearer. I need to render a partial dynamically based on a previous selection box.
REQUEST belongs to PRODUCT
PRODUCT belongs to CATEGORY
CATEGORY has many PRODUCTS
PRODUCT has many REQUESTS
User hits form: create_request.html.erb
User selects a category, then the products select list is populated (like Railscast 88 - dynamic select boxes)
What I now need is to render different partial forms based on which product is selected. I suck at jquery.
create_request.html.erb:
<%= javascript_include_tag "dynamic_products.js" %>
<% form_for :request, :url => {:controller => :requests, :action => :create_request, :id => params[:id]} do |f| %>
<label>Select Category:</label>
<%= select( "request", "category_id", Category.find( :all).collect { |c| [c.name, c.id] })%></br>
<div id="product_field">
<label>Select Product</label>
<%= select( "request", "product_id", Product.find( :all).collect { |p| [p.name, p.id] })%></br>
</div>
#### and here is where I need help:
#### if request.product_id = 1, render partial _form1
#### if request.product_id = 2, render partial _form2
<button type="submit">Submit</button>
<% end %>
dynamic_products.js.erb:
var products = new Array();
<% for product in #products -%>
products.push(new Array(<%= product.category_id %>, '<%=h product.name %>', <%= product.id %>, <%= product.active %>));
products.sort()
<% end -%>
function categorySelected() {
category_id = $('request_category_id').getValue();
options = $('request_product_id').options;
options.length = 1;
products.each(function(product) {
if (product[0] == category_id && product[3] == 1) {
options[options.length] = new Option(product[1], product[2]);
}
});
if (options.length == 1) {
$('product_field').hide();
} else {
$('product_field').show();
}
}
document.observe('dom:loaded', function() {
categorySelected();
$('request_category_id').observe('change', categorySelected);
});

Answer 1

one reminder first before we start. I'm not sure about this but I think request is a reserved word in rails.
JS
this just observes the dropdown and performs an ajax call
$(document).ready(function() {
$('#request_product_id').change(function() {
$.ajax({ url: '/products/' + this.value + '/form_partial' });
});
});
ROUTES
nothing fancy here either. Just setting up a route where the ajax will go to when it is triggered
resources :products do
get :form_partial, on: :member
end
CONTROLLER
we just fetch the product using :id which is passed from ajax
def form_partial
#product = Product.find params[:id]
end
JS TEMPLATE
you need to create a form_partial.js.erb which will render the partial depending on the product. The code below appends the partial after the product_field div
# app/views/products/form_partial.js.erb
$('#product_partial').remove();
<% if #product.id == 1 %>
$('#product_field').after('<div id="product_partial"><%= escape_javascript render('partial1') %></div>');
<% else %>
$('#product_field').after('<div id="product_partial"><%= escape_javascript render('partial2') %></div>');
<% end %>
UPDATE: for rails 2.x
we just need to change the routes and the js template in order for this to run on rails 2.x
ROUTES 2.x
map.resources :products, member: { form_partial: :get }
JS TEMPLATE 2.x
if I remember correctly, the file should be named form_partial.js.rjs. This will give you a page variable which you can use to add js.
# app/views/products/form_partial.js.rjs
page << "$('#product_partial').remove();"
page << "<% if #product.id == 1 %>"
page << " $('#product_field').after('<div id="product_partial"><%= escape_javascript render('partial1') %></div>');"
page << "<% else %>"
page << " $('#product_field').after('<div id="product_partial"><%= escape_javascript render('partial2') %></div>');"
page << "<% end %>"