Question

I keep getting a undefined method 'comments' for nil:NilClass in my create method when I try to create a new comment(polymorphic relationship). I’ve browsed several other questions regarding this and can’t seem to locate what’s wrong with my form/controller.

Here is my generic partial for comments:

<%= form_for [@commentable, Comment.new] do |f| %>
  <%= f.text_area :content %>
  <%= f.submit "Post" %>
<% end %>

Please note that this is rendered in my traveldeal/show page. The form renders fine. If I change the form_for to pass parameters [@commentable, @comment], I get the error undefined methodmodel_name’ for NilClass:Class`

routes.rb

resources :users 
resources :traveldeals

resources :traveldeals do
  resources :comments
end

resources :users do
  resources :comments
end

The Railscasts has the above written as resources :traveldeals, :has_many => :comments, but I believe this is dated syntax.

comments_controller.rb

class CommentsController < ApplicationController
  before_filter :authenticate, :only => [:create, :destroy]

  def new
    @comment = Comment.new
  end

  def create
    @commentable = find_commentable
    @comment = @commentable.comments.build(params[:comment])
    @comment.user_id = current_user.id

   if @comment.save
      flash[:success] = "Successfully saved comment."  
      redirect_to root_path
    else
      redirect_to current_user
    end
  end

private

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

end

Edit: Added the solution so the code above works for me.

Answer 1

You have @commentable in your form_for, but where is that variable set? It seems to be set nowhere and I think that is the cause of the error. Also see my answer to your other question.