Ruby on Rails. Views in polymorphic associations - ruby-on-rails

Question

I develop site which has articles and news pages and I would like to add opportunity to comment both. I use polymorphic associations.
class Article < ActiveRecord::Base
has_many :commentaries, :as => :commentable
end
class News < ActiveRecord::Base
has_many :commentaries, :as => :commentable
end
class Commentary < ActiveRecord::Base
belongs_to :commentable, :polymorphic => true
end
I would like to show comments below commentable object
views/articles/show.html.erb
<p>
<b>Title:</b>
<%= #article.title %>
</p>
<p>
<b>Short text:</b>
<%= #article.short_text %>
</p>
<p>
<b>Full text:</b>
<%= #article.full_text %>
</p>
<%= render 'commentaries/form' %>
views/news/show.html.erb
<p>
<b>Title:</b>
<%= #news.title %>
</p>
<p>
<b>Text:</b>
<%= #news.text %>
</p>
<p>
<b>Created:</b>
<%= #news.created %>
</p>
views/commentaries/_form.html.erb
<h1>Comments</h1>
<ul id="comments">
<% #commentaries.each do |comment| %>
<li><%= comment.content %></li>
<% end %>
</ul>
<h2>New Comment</h2>
<% form_for [#commentable, Comment.new] do |form| %>
<ol class="formList">
<li>
<%= form.label :content %>
<%= form.text_area :content, :rows => 5 %>
</li>
<li><%= submit_tag "Add comment" %></li>
</ol>
<% end %>
And my controllers:
class CommentariesController < ApplicationController
def index
#commentable = find_commentable
#commentaries = #commentable.commentaries
end
end
class ArticlesController < ApplicationController
def show
#article = Article.find(params[:id])
end
end
When I go to mysite/article/1 I get error undefined method `each' for nil:NilClass, because there isn't #commentable in my article controller and commentaries controller's code doesn't execute.
How to execute index action of commentaries controller on article/show page?

Answer 1

Add local variable:commentable => #article, while rendering the commentaries form
<%= render 'commentaries/form', :commentable => #article %>
Access the local variable from you partial view views/commentaries/_form.html.erb
<% commentable.commentaries.each do |comment| %>
...
<% end %>
...
<% form_for [commentable, Comment.new] do |form| %>
...
<% end %>