Controller Namespaces and Routing issue

I created a routing test rails3 app with one model 'User':

rails new routing_test_app
rails generate model User name:string
rails generate scaffold_controller admin/user
rake db:migrate

Added to routes.db:

namespace :admin do
  resources :users
end

rake routes

admin_users GET    /admin/users(.:format)          {:action=>"index", :controller=>"admin/users"}
admin_users POST   /admin/users(.:format)          {:action=>"create", :controller=>"admin/users"}
new_admin_user GET    /admin/users/new(.:format)      {:action=>"new", :controller=>"admin/users"}
edit_admin_user GET    /admin/users/:id/edit(.:format) {:action=>"edit", :controller=>"admin/users"}
admin_user GET    /admin/users/:id(.:format)      {:action=>"show", :controller=>"admin/users"}
admin_user PUT    /admin/users/:id(.:format)      {:action=>"update", :controller=>"admin/users"}
admin_user DELETE /admin/users/:id(.:format)      {:action=>"de开发者_开发百科stroy", :controller=>"admin/users"}

views/admin/users/_form.html.erb

<%= form_for(@admin_user) do |f| %>
  <% if @admin_user.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@admin_user.errors.count, "error") %> prohibited this admin_user from being saved:</h2>

      <ul>
      <% @admin_user.errors.full_messages.each do |msg| %>
        <li><%= msg %></li>
      <% end %>
      </ul>
    </div>
  <% end %>
    <%= f.text_field :name %>
  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

When I go to 'http://localhost:3000/admin/users/new' rails throws an error:

undefined method `users_path' for #<#<Class:0x0000010116ca90>:0x000001011588d8>

Extracted source (around line #1):

1: <%= form_for(@admin_user) do |f| %>
2:   <% if @admin_user.errors.any? %>
3:     <div id="error_explanation">
4:       <h2><%= pluralize(@admin_user.errors.count, "error") %> prohibited this admin_user from being saved:</h2>

---

That's because @admin_user is a User object, so Rails guesses the URL helper to be users_path. It's a simple fix. Just replace @admin_user form_for param with [:admin, @admin_user]. You might also want to rename the instance variable @user for less repitition. Having to use the array is a drawback of using namespaces, so one should always take that into consideration.

---

The form_for method will not guess nested routes. Try this:

form_for [:admin, @admin_user] do |f|