Problem with polymorphic association in Rails

Question

I am trying to follow Ryan Bates screencast but have an error message. I did the following:

1) Create table

class CreateComments < ActiveRecord::Migration
  def self.up
    create_table :comments do |t|
      t.references :commentable, :polymorphic => true

2) Setup models

class Comment < ActiveRecord::Base
  belongs_to :commentable, :polymorphic => true

class Product < ActiveRecord::Base
  has_and_belongs_to_many :categories
  has_many :comments, :as => :commentable

class Category < ActiveRecord::Base
  has_and_belongs_to_many :products
  has_many :comments, :as => :commentable

3) Change controller show action

class CategoriesController < ApplicationController
  def show
    @category = Category.find_by_permalink(params[:id])
    @commentable = @category
    @comment = Comment.new(:commentable => @category)
  end

4) Add a form to template views/categories/show.html.erb

<% form_for [@commentable, Comment.new] do |f| %>
  <p>
    <%= f.label :name %><br />
    <%= f.text_field :name %>
  </p>
  <p>
    <%= f.label :content %><br />
    <%= f.text_area :content %>
  </p>
  <p>
    <%= f.submit 'Submit' %>
  </p>
<% end %>

5) After that I get error message by accessing /categories/my-category-permalink

NoMethodError in Categories#show
undefined method `category_comments_path' for #<ActionView::Base:0x69a9254>

Could you help me to understand what I did wrong? In the original screencast Ryan accesses comments by /categories/permalink/comments using nested associations, but I don't need that. I want to write comments directly from my polymorphic objects. Thanks

Answer 1

The problem was in routes settings. I thought that since I don't use nested resources, I can keep routes unchanged. Well, now I know that I was wrong... :) Add this to fix the problem:

map.resources :categories :has_many => :comments
map.resources :products, :has_many => :comments