polymorphic association

gistfile1.rb

# models/comment.rb

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

# models/post.rb
class Post < ActiveRecord::Base
  belongs_to :post_category
  belongs_to :user
  
  has_many :comments, :as => :commentable  
end

# models/user.rb
class User < ActiveRecord::Base
  has_many :comments
  has_many :posts
  
end


# controllers/comments_controller.rb

class CommentsController < ApplicationController
  before_filter :authenticate_user!

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

  def show
    @comment = Comment.find(params[:id])
  end

  def new
    @comment = Comment.new
  end

  # GET /comments/1/edit
  def edit
    @comment = Comment.find(params[:id])
  end

  # POST /comments
  # POST /comments.json
  def create
    @commentable = find_commentable 
    @comment = @commentable.comments.build(params[:comment])
    if @comment.save
      redirect_to @comment, :notice => 'Comment was successfully created.'
      redirect_to :id => nil 
    else
      render :action => "new"
    end
  end

  def update
    @comment = Comment.find(params[:id])
    if @comment.update_attributes(params[:comment])
      redirect_to @comment, :notice => 'Comment was successfully updated.' 
    else
      render :action => 'edit'
      
    end
  end

  # DELETE /comments/1
  # DELETE /comments/1.json
  def destroy
    @comment = Comment.find(params[:id])
    @comment.destroy
    redirect_to comments_url, :message => 'Comment deleted.'
  end
  
  # find commentable (parent) item
  def find_commentable  
    params.each do |name, value|  
      if name =~ /(.+)_id$/  
        return $1.classify.constantize.find(value)  
      end  
    end  
    nil  
  end
  
end


# view partial (haml)
= form_for [@commentable, Comment.new], :remote => true do |f|
	#new_comment.add_comment
		= f.hidden_field :user_id, :value => current_user.id
		= f.text_field :content, :size => 55,  :value => 'leave a comment...', :onfocus => 'this.select()', :class => 'comment_form'
		= f.submit "send"