Question

having a lot of trouble setting up polymorphic. I have Comments which works fine, but the Links which should work exactly the same has NameError in Links#index. If I try to forum_posts/1/comments all is good but not forum_posts/1/links.

I was following the railscast tutorial http://railscasts.com/episodes/154-polymorphic-association?view=asciicast

Appreciate the help.

Error

NameError in Links#index

uninitialized constant ForumPost::Link
Extracted source (around line #4):

1: <h1>Links</h1>
2: 
3: <ul id="links">
4:   <% @links.each do |link| %>
5:     <li><%= link.display_name %></li>
6:   <% end %>
7: </ul>

routes

resources :forum_posts do
  resources :comments
  resources :links
end

Models

*models/forum_posts.rb*

class ForumPost < ActiveRecord::Base
  attr_accessible :content, :display_name, :section, :user_id
  has_many :comments, :as => :commentable
  has_many :links, :as => :linkable
end

models/comments.rb

class Comment < ActiveRecord::Base
  attr_accessible :commentable_id, :commentable_type, :content, :user_id
  belongs_to :commentable, :polymorphic => true
end

models/comments.rb

class Links < ActiveRecord::Base
  attr_accessible :description, :display_name, :inamge, :linkable_id, :linkable_type,    :user_id
  belongs_to :linkable, :polymorphic => true
end

Controllers

*controllers/comments_controller.rb*

class CommentsController < ApplicationController

  def find_commentable
    params.each do |name, value|
      if name =~ /(.+)_id$/
        return $1.classify.constantize.find(value)
      end
    end
    nil
  end

  def index
    @commentable = find_commentable
    @comments = @commentable.comments
  end

  def create
    @commentable = find_commentable
    @comment = @commentable.comments.build(params[:comment])
    if @comment.save
      flash[:notice] = "Successfully saved comment."
      redirect_to :id => nil
    else
      render :action => 'new'
    end
  end

end

*controller/links_controller.rb*

class LinksController < ApplicationController

  def find_linkable
    params.each do |name, value|
      if name =~ /(.+)_id$/
        return $1.classify.constantize.find(value)
      end
    end
    nil
  end

  def index
    @linkable = find_linkable
    @links = @linkable.links
 end

 def create
   @linkable = find_linkable
   @link = @linkable.links.build(params[:link])
   if @link.save
     flash[:notice] = "Successfully saved link."
     redirect_to :id => nil
   else
     render :action => 'new'
   end
  end

end

Views

views/comments/index.html.erb

<h1>Comments</h1>

<ul id="comments">
  <% @comments.each do |comment| %>
    <li><%= comment.content %></li>
  <% end %>
</ul>

<h2>New Comment</h2>
<%= form_for [@commentable, Comment.new()] do |form| %>
  <%= form.label :content %><br/>
  <%= form.text_area :content, :rows => 5 %><br/>
  <%= form.submit "Add comment" %>
<% end %>

views/links/index.html.erb

<h1>Links</h1>

<ul id="links">
  <% @links.each do |link| %>
    <li><%= link.display_name %></li>
  <% end %>
</ul>

<h2>New Link</h2>
<%= form_for [@linkable, Link.new()] do |form| %>
  <%= form.label :display_name %><br/>
  <%= form.text_area :display_name %><br/>
  <%= form.submit "Add link" %>
<% end %>

Answer 1

Your Links model should be placed at app/models/link.rb and should be called Link, not Links.