Friendly_id not working, redirects to Category with wrong index

Question

I've followed Ryan Bates' screencast in order to get friendly_id set up (up until the def should_generate_new_friendly_id? part) for my Category model. One of the Categories is books, but for some reason /categories/books redirects to a blank page, and the log shows that the server is trying to fetch a category with id=0 (which is wrong.) So here's what I've done:

class Category < ActiveRecord::Base
  extend FriendlyId
  friendly_id :name, use: :slugged

  validates :name, :presence => true, :uniqueness => true, :length => { :in => 3..20 }
end

My migration:

class AddSlugToCategories < ActiveRecord::Migration
  def change
    add_column :categories, :slug, :string
    add_index :categories, :slug
  end 
end

And last but not least, in rails console:

Category.find_each(&:save)

Any idea what the problem could be?

Edit:

Started GET "/categories/books" for 127.0.0.1 at 2012-03-02 13:03:29 -0500
  Processing by CategoriesController#show as HTML
  Parameters: {"id"=>"books"}
  Category Load (0.4ms)  SELECT "categories".* FROM "categories" 
  Item Load (0.6ms)  SELECT "items".* FROM "items" WHERE "items"."category_id" = 0
Rendered categories/_items.html.erb (1.9ms)
Rendered categories/show.html.erb within layouts/application (20.7ms)
Completed 200 OK in 139ms (Views: 69.1ms | ActiveRecord: 6.6ms)

Answer 1

This turned out to be more than just friendly_id ... (see comments on original question)

It seems as though the category#show action is missing:

Category.find(params[:id])