acts_as_commentable examples?

Lets assume a Post model. Make sure, you have

class Post < ActiveRecord::Base
acts_as_commentable
end

then in the view of say Post#show

  <%= form_tag "/posts/add_new_comment" do %>
    <%= hidden_field_tag "id", post.id %>
    <%= text_area_tag "comment[comment]" %>
    <%= submit_tag "Post Comment" %>
  <% end %>

then in the PostController

  def add_new_comment
    post = Post.find(params[:id])
    post.comments << Post.new(params[:comment])
    redirect_to :action => :show, :id => post
  end

and in routes.rb

  match "/posts/add_new_comment" => "posts#add_new_comment", :as => "add_new_comment_to_posts", :via => [:post]

Hope this gets u up and running.

This is very, very basic stuff and you clearly need some better structure and approach to your learning. Buying a book, such as Agile Web Development with Rails, is the only real way to learn, otherwise you'll wander from problem to problem without ever actually learning anything well.

Say you have a post that you want to comment.

#routes.rb
map.resources :posts do |post|
  post.resources :comments
end

#post_controller.rb
def show
  @post.find params[:id]
  @comment = @post.comments.new
end

#posts/show.html.erb
<%- form_for [@post, @comment] do |f|-%>
  <%= f.text_area :body -%>
  <%= f.submit -%>
<%- end -%>

#comments_controller
def create
  @post = @post.find params[:post_id]
  @comment = @post.comments.new params[:comment]
  if @comment.save
    redirect_to @post

This is an old question, but I want to throw in my solution as well as the gem's README is still unhelpful after all these years. It builds upon @Kunday's answer. The following will be a tutorial to use the act_as_commentable gem to...

1. Allow users to create comments under each post.
2. Show all comments belonging to a post.

This assumes that you already have a working "blog", whether it be pictures or posts. Install gem, then run rails g comment to get started.

Allow users to create comments under each post.

First, inside the model that you want to use commentable gem, add the following line as suggested in the gem's README.

class Post < ActiveRecord::Base 
  acts_as_commentable
end

Then create a new comment controller with the create action. Please note that the :authenticate_user! is part of devise which is a gem for creating easy authentication. current_user is also part of devise as a helper. It is needed if you want to display the user's name/email under the comment body.

class CommentsController < ApplicationController
  before_action :authenticate_user!

  def create
    post = Post.find_by(id: params[:id])
    comment = post.comments.build(comment_params)
    comment.user = current_user

    if comment.save
      flash[:notice] = "Comment has been created."
      redirect_to post
    else
      flash[:alert] = "Comment has not been created."
    end
  end

  private    
    def comment_params
      params.permit(:comment)
    end
end

Next, set up the routes. It's just this. This means that when someone sends a post request to comments, we will run to create action inside the comments controller.

post 'comments' => 'comments#create', as: "create_comment"

The as: "create_comment" gives it an alias, so you can do create_comment_path. Now, on the show view of Post, we'll add the form. The divs will help you add css.

<div class="comment-section">
  <%= form_tag create_comment_path, method: "post" do %>
    <%= hidden_field_tag "id", @post.id %>
      <%= text_area_tag :comment %>
      <%= submit_tag "Submit" %>
    <% end %>
</div>

Now to show each comment under the Post show view.

The divs will help you add css, comment.user.name will work if your User class has a name column. Else, change it to email or whatever identifier you choose to use.

<div class="comment_list">
  <% @comments.each do |comment| %>
    <%= comment.comment %> <br>
      <%= comment.user.name %> <br>
        <br>
    <% end %>
</div>

And finally, in order for @comments to exist in the show page, go to your Post controller, and under show, add the following:

  def show
    @post = Post.find_by(id: params[:id])
    @comments = @post.comments.all
  end

This should be good for the requirements. Good luck.