categories_controller.rb

class CategoriesController < ApplicationController

  def new
    @category = current_user.categories.build
    @categories = current_user.categories   
  end
  
end

log

Started GET "/categories/new" for 127.0.0.1 at 2013-04-30 22:32:15 -0400
Processing by CategoriesController#new as HTML
  User Load (0.5ms)  SELECT "users".* FROM "users" WHERE "users"."id" = 1 LIMIT 1
  Rendered shared/_error_messages.html.erb (0.0ms)
  Rendered categories/_form.html.erb (1.8ms)
   (0.3ms)  SELECT COUNT(*) FROM "categories" WHERE "categories"."user_id" = 1
  Category Load (0.3ms)  SELECT "categories".* FROM "categories" WHERE "categories"."user_id" = 1
  Rendered categories/new.html.erb within layouts/application (5.8ms)
Completed 500 Internal Server Error in 10ms

ActionController::RoutingError (No route matches {:action=>"edit", :controller=>"categories", :id=>#<Category id: nil, name: nil, created_at: nil, updated_at: nil, user_id: 1>}):
  app/views/categories/new.html.erb:9:in `block in _app_views_categories_new_html_erb__3219152364255558243_70124608600680'
  app/views/categories/new.html.erb:7:in `_app_views_categories_new_html_erb__3219152364255558243_70124608600680'

new.html.erb

<h1>New Category</h1>

<%= form_for @category do |f| %>
  <%= render 'shared/error_messages', object: f.object %><br>
  <%= f.label :name %><br>
  <%= f.text_field :name %><br>  
  <%= f.submit "+category" %><br>
<% end %>

<% if @categories.any? %>
<ul>
  <% @categories.each do |category| %>
    <li>
	  <%= category.name %> | <%= link_to 'Change', edit_category_path(category) %>
	</li>    
  <% end %>
</ul>
<% end %>