dynamic menu

_category.html.erb

<div id="category_select">
	<p id="subcategory_field">
	  <label for="subcategory">Subcategory</label><br/>
	  <%= f.collection_select :category_id, @subcategory ,:id,:name,:prompt => "Select Subcategory"%>
	</p>
 </div>

_form.html.erb

    <p>
      <label for="category">Category</label><br/>
      <%= f.collection_select :category, Category.find_all_by_parent_id(nil) ,:id,:name,:prompt => "Select category"%>
    </p>
     

        <%= render :partial => 'category', :locals => { :f => f , :categoryID => @subcategory} %>
     

    #if without :partial ,it will give me error ,f is undefined method
    #if with :partial, it give me  nil object when you didn't expect it!
 

application.js

$(document).ready(function () {

  $('#subcategory_field').hide();

  $('#product_category').change(function () {
	   	$('#subcategory_field').show();

	   	data = $('#product_category').val();
	   	
	   	jQuery.ajax({
	  		url: '/javascripts/dynamic_subcategory/',
	  		type: 'GET',
	  		data: {"categoryID" : data}
		});
	   return false;
  });
});



#no changes

Category.rb

class Category < ActiveRecord::Base
	acts_as_nested_set
	accepts_nested_attributes_for :children
	
	attr_accessible :name, :parent_id
	attr_protected :lft, :rgt
	
	has_many :products
end

console server errors

Started GET "/products/new" for 127.0.0.1 at 2012-06-30 04:12:43 -0400
  Processing by ProductsController#new as HTML
  SQL (0.3ms)   SELECT name
 FROM sqlite_master
 WHERE type = 'table' AND NOT name = 'sqlite_sequence'
  Category Load (0.4ms)  SELECT "categories".* FROM "categories" WHERE "categories"."parent_id" IS NULL
Rendered products/_category.html.erb (5.1ms)
Rendered products/_form.html.erb (159.5ms)
Rendered products/new.html.erb within layouts/application (160.5ms)
Completed 500 Internal Server Error in 221ms

ActionView::Template::Error (You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.map):
    1: <div id="category_select">
    2: 	<p id="subcategory_field">
    3: 	  <label for="subcategory">Subcategory</label><br/>
    4: 	  <%= f.collection_select :category_id, @subcategory ,:id,:name,:prompt => "Select Subcategory"%>
    5: 	</p>
    6:  </div>
  app/views/products/_category.html.erb:4:in `_app_views_products__category_html_erb___771868271907344220_33660280_35256791884167728'
  app/views/products/_form.html.erb:20:in `block in _app_views_products__form_html_erb__4356573898125156143_34174760__1131280712954032946'
  app/views/products/_form.html.erb:5:in `_app_views_products__form_html_erb__4356573898125156143_34174760__1131280712954032946'
  app/views/products/new.html.erb:3:in `_app_views_products_new_html_erb___4226790253553222994_34189920_4007620194630562797'
  app/controllers/products_controller.rb:31:in `new'

Rendered /home/nicholas/.rvm/gems/ruby-1.9.2-p320/gems/actionpack-3.0.9/lib/action_dispatch/middleware/templates/rescues/_trace.erb (1.1ms)
Rendered /home/nicholas/.rvm/gems/ruby-1.9.2-p320/gems/actionpack-3.0.9/lib/action_dispatch/middleware/templates/rescues/_request_and_response.erb (2.8ms)
Rendered /home/nicholas/.rvm/gems/ruby-1.9.2-p320/gems/actionpack-3.0.9/lib/action_dispatch/middleware/templates/rescues/template_error.erb within rescues/layout (6.9ms)

dynamic_subcategory.js.erb

$('category_select').replaceWith('<%= escape_javascript(render => 'products/category', :locals => {:f => f,:categoryID => @subcategory}) %>')

#added :f => f

javascripts_controller.rb

class JavascriptsController < ApplicationController
	respond_to :js

	def dynamic_subcategory
		@subcategory = Category.find(params[:categoryID]).children

		respond_with(@subcategory) # This will return dynamic_subcategory.js.erb
	end

end
i change responde_with :js  to respond_to :js


#when i load the page,it return me You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.map and error come from 
  <%= f.collection_select :category_id, @subcategory,:id,:name,:prompt => "Select Subcategory"%>

,i see the terminal, and it dint load my js files.

this is working?