Question

I am working on my first polymorphic association relationship and I am having trouble refactoring my form_for create comments.

I tried going through the Polymorphic Association RailsCasts http://railscasts.com/episodes/154-polymorphic-association?view=asciicast, but it seems dated.

I have two questions:

1. How do I rewrite my comment_form partial so that it would work for anything commentable? The way I have it right now, it would only work for traveldeals since (:commentable_id => @traveldeal.id).

2. When I create the comment, the commentable_type is empty. What is commentable_type and do I need to pass it in the form?

Thanks!

user.rb

class User < ActiveRecord::Base
  has_many :comments, :dependent => :destroy
end

traveldeal.rb

class Traveldeal < ActiveRecord::Base
  has_many :comments, :as => :commentable, :dependent => :destroy
end

comment.rb

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

  validates :user_id, :presence => true
  validates :commentable_id, :presence => true
  validates :content, :presence => true
end

traveldeal_show.html.erb

<%= render 'shared/comment_form'  %>

_comment_form.html.erb

<%= form_for current_user.comments.build(:commentable_id => @traveldeal.id) do |f| %>
  <%= render 'shared/error_messages', :object => f.object %>

<div>
  <%= f.text_area :content %>
</div>

<%= f.hidden_field :user_id %>
<%= f.hidden_field :commentable_id %>

<div>
  <%= f.submit "Add Comment" %>
</div>
<% end %>

comments_controller.rb

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

  def create
    @comment = Comment.new(params[:comment])
    @comment.save
    redirect_to root_path
  end

end

Answer 1

The only part that is dated in the Railscast are the routes.

To answer your first question: create your form like it is done in the Railscast:

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

If you do it like this commentable_type will be set automatically. You need the type so you know to what model a comment belongs. Note that you have to set @commentable in the method where you use the comment form.

E.g.

class TraveldealsController < ApplicationController
  def show
    @traveldeal = @commentable = Traveldeal.find(params[:id])
  end
end