How to Build Forums in Rails 3

This tutorial will go over the basic steps to create a forums app. The forums will extend from my previous blog post about integrating Rails 3 with AuthLogic. If you are new to rails I’d high recommend reading it, otherwise continue. First download the source code from the AuthLogic App and move the code to more logically named directory for this project.

$ mkdir forums
$ git init
$ git clone git:// forums
$ cd forums
$ rake db:migrate
$ rails -s

Feel free to verify that everything is working, you should be able to register and login at /users.

The Backend

Rails has reserved “thread” has a model name so this will create a weird model name but the other two model names are straight forward: Board, Conversation, Comment.

Board is a set of boards, groupings of conversations. Conversation, probably more commonly referred to as “Thread”, is list of Comments made by users. In our forum we’ll keep it simple, A Board will contain only a name and an id, a Conversation will belong to a board. A Conversation will have a title and a creating user. Comments will have only a body a posting user and a reference to the conversation they belong to.

$ rails g scaffold board id:integer title:string
$ rails g scaffold conversation id:integer title:string board_id:integer user_id:integer
$ rails g scaffold comment id:integer user_id:integer conversation_id:integer body:text

This created all the controllers, views, models, and migration files needed. Open up the three migration files created, and edit them to look as follows.

These changes add indexes to our Conversations and Comments tables. These will add a much needed performance boost when querying the database. They also added size limitations to board.title and conversation.title of 50 characters.

Now create the database tables by running:

$ rake db:migrate

Some Quick Backend Additions

Feel free to browse around the site, you’ll notice all the forms work correctly, but none of the objects are linked together. To tell active record that these models are linked we must edit the Model Classes.
Open up your newly created model classes and edit them to look like this:

In this we see two very important ideas. We’ve added form validation as well as ORM hooks that define relationships between our models. In board.rb and conversation.rb we added has_many :conversations and has_many :comments, respectively, this informs Rails these are 1 to many relationships. You can see the rails docs for has_many here. This makes the relationship from one conversation to many comments. In conversation.rb and comments.rb you can see the belongs_to function, this function tells rails that these objects belong to another specific object, you can see the docs for belongs_to here.
validates_presence_of is called when a save, update, or create are called on an object. This function makes sure that there is data stored in these member variables. We specified that conversation.title and comment.body must be required, we don’t want any empty posts. Board.title was purposefully skipped, it is not for general use.

If you navigate to your conversations page: http://localhost:3000/conversations and try to create a message, not including a title, you will get a nice error saying that it is a required field. You will how ever notice that you can make this field as long as you like even though we specified it should only be 50 characters long. Lets fix this, add the following line of code to your conversation.rb file:

validates_length_of :title, :maximum=>50

If you try again you will see an error message stating that the “the input must be less than 50 characters”.

If you’ve created any data, you may want to clean it up now, it may cause problems later in this demonstration.


Now that we have the backend in order, lets create the routes needed to use this message board. Open up your config/routes.rb file and change it to look like this:

Delete your public/index.html file, it’s no longer needed.

Now localhost:3000/ will display a list of your Boards, instead of the rails information page.

In your console type:

$ rake routes

This is a list of every url that your app can handle, the most important are the top few. We’ve now created a url hierarchy. All of a conversations will be listed by /boards/:board_id/conversations/:id.

Jumping into the view

Our site looks okay, but lets try and spiff it up a bit. Open up your views/layouts/index.html and change it to look like:

Create a new file in public/stylesheets called style.css and copy this style sheet,


At localhost:3000 you should be greeted by a much friendlier page:

If you haven’t created a board yet, feel free to create one now using the “Create Board” Link at the bottom of the page. You can put in you own ID if you want, if you leave it blank rails will auto increment the id.

Lets fix up that homepage a bit and make it look slightly more professional. Open up views/boards/index.html, and change it to look like this:

Now that our landing page looks decent, lets see what happens when we view our message board:


Not what anybody envisions a messageboard to be looking like, lets make some quick cosmetic changes before moving into the controller. Open up app/views/boards/show.html.erb and make it the following changes:

As you can see here we added a “Post New Message” link, the url function did not come out of thin air, if you run rake routes again. You’ll see there is a path named “new_board_conversation”, you can use any of those as a url by appending _url or _path to them.

If you click on the link to post new message you’ll get “No Routes Matches” error. We’ll fix that in a minute, but first lets make some adjustments to our conversation controller, open up app/controllers/conversation.rb and make the follow changes:

We added a private function that tries to load a Board off a passed in parameter. This function will be called on any page that goes through this controller.

Modify AuthLogic

If you have tried to login you may have noticed that we skipped a step. The login, logout, and register functions are not exactly tied to our application. To fix this we need to correct links in the views and redirect the controllers. While we’re doing this it will be a good time to remove functions that the app won’t be using. Open up app/controllers/users_controller.rb and edit it to look like so:

In this controller we added a function is_user. This function determines if the user is logged in and they are the correct user to be viewing specific pages. We also changed redirect urls to the site homepage and removed a lot of unused code. Now lets update our User View: We’ll have to change the links on all the pages as well as display less confidential information on the Profile page.

Now we just have to fix the Login view and the login/logout controller. These files need to have some cosmetic changes and fix issues with redirects open up app/views/user_sessions/new.html.erb and app/controllers/user_sessions_controller.rb and edit them to look like the following:

Now we just changed all the automatic form rerouting to point to our default homepage, added some basic styling, and changed the links in the site to point to more logical places. Lets create some content

Creating a New Post

There are four parts to our new posts: author, board, title, body. Author will be determined by the user_session, board will be determine through the URL, what our form needs to get from the user is title and body. We must modify the Conversation controller to create a Comment object which we can use in the view.
Open up app/controllers/conversation.rb and modify create and new functions to look like this:

The build function was automatically created when we used has_many :comments in the model, it creates an unsaved object using default values. In the create function we’ve added the board and author variable assignment, we also check to see if the user is logged in before we save.

if current_user &&

We create @comment in both places for simplicity. Both of these function use the same view, create if there is an error and new by default, thus we need the same variables in scope. In the create function we pass in params[:comment] to build, this will build a Comment object with any data passed in the comment parameter.

Now lets setup our views, change app/views/conversations/index.html.erb, app/views/conversations/_form.html.erb to look like this:

<%= form_for(@conversation, :url => board_conversations_path) do |f| %>
  <% if @conversation.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@conversation.errors.count, "error") %> prohibited this conversation from being saved:</h2>

      <% @conversation.errors.full_messages.each do |msg| %>
        <li><%= msg %></li>
      <% end %>
  <% end %>

  <div class="field">
    <%= f.label :title %><br />
    <%= f.text_field :title %>

  <%= fields_for(@comment) do |cf|%>
  <div class="field">
    <%= cf.label :body %><br />
    <%= cf.text_area(:body, :size => "60x10")%>
  <% end %>

  <div class="actions">
    <%= f.submit :as => "Create Post"%>
<% end %>
<h1 id="page_title">New conversation</h1>
<%= link_to @board.title, @board %>

<%= render 'form' %>

<%= link_to @board.title, @board %>

The changes to new.html.erb are fairy straight forward. We added an id to the h1 tag, and changed the link to display the name of the current table and link to the current table. We modified_form.html.erb pretty heavily, we removed alot of the input fields that will be assigned in the controller. We also modified the error printing at the top to include any errors from @comment. fields_for works like form_for but does not create a new form tag. This allows us to create fields that are related to other objects.

Lets create our first post. When you’re done it should look something like this:

[img new_post.jpg]

Viewing Our Post

You may be wondering where your posts are? Clearly they’re in the database but they’re not showing up in our view. Lets fix that, open up app/views/boards/show.html.erb

We display all the conversations in that board along with some basic meta data. Most of this code is rather straight forward, the link to uses one of the routes that can be easily found using $ rake routes . We use the find function which was also provided when we used has_many. We subtract one for the number of replies so that we do not count the post it self. But all in all this view is as straight forward as they come.

Now lets work on the message view itself. Open up app/views/conversation/show.html.erb and edit to look like this:

Once again nothing to exciting happening here, the more astute of you may have realized we created a url function that we don’t currently have mapped. Lets create that route, add

get '/boards/:board_id/conversations/:id/reply' => "conversations#reply", :as => :reply_board_conversation
post '/boards/:board_id/conversations/:id/reply' => "conversations#save_reply", :as => :reply_board_conversation

This will create two different url matches, one for GET requests and one for POST, one when the page is called and one when the form is submitted.
Lets got and create the reply and save_reply functions in the conversation controller, they should look fairly similar to the new and create functions, or like these:

Once again here nothing is too revolutionary. reply handles the page load. It creates a @conversation and @comment for use in the view to generate forms. The @conversation is loaded from the url, as is a @board. @comment is empty. save_reply handles POST requests, so form submissions. It verifies that the user is logged in and that the parent conversation exists. It then creates the comment from the conversation, assigns the user, and assigns the values passed in from the form. It saves the data and redirects the user to the board overview with a friendly reminder.

Reply function uses reply.html.erb as it’s view, since that hasn’t been created yet lets do that now. Create another file as well _reply_form.html.erb. They should look like this:

There is nothing we haven’t seen before in these files by themselves. Reply.html.erb includes _reply_form.html.erb you can tell this by the render statement, ‘reply_form’ is prepended with ‘_’ so you know it’s not a controller view. _reply_form.html.erb uses the same action as we saw to generate the url to this page, and only has a text area input field.

Feel free to try it now out now. The complete forum/message board should be working. If you have any questions feel free to leave a comment or view the working code base on my GitHub For Rails boards

  • todd

    i dont kno what i am doing wrong but

    get ‘/boards/:board_id/conversations/:id/reply’ => “conversations#reply”, :as => :reply_board_conversation
    post ‘/boards/:board_id/conversations/:id/reply’ => “conversations#save_reply”, :as => :reply_board_conversation

    isn’t showing up. please help. this post was a huge help. thank you.

  • Flashing Beacon %0B

    :,- I am very thankful to this topic because it really gives up to date information -.~

  • David Silva

    Thank you for your explanation.

    At the beginning you could do:

    git clone git:// folder

    then you should do bundle install
    and finally rake db:migrate and rails s

  • Stef

    Dear Logan,

    Thanks very much for your fantastic & useful tutorials !!! 8-)
    I really enjoyed your explanations and tried to reuse these in an application I would like to develop for myself (website to be developped in the framework of a training course/ complementary studies)

    I unfortunately encountered some problems while trying to finalise my app…

    The following routing message appears while trying to register or login the app :
    “undefined local variable or method `homepage_url’ ”
    (among other files: /app/views/users/new.html.erb where line #5 & app/views/users/show.html.erb where line #16)

    Could you please help me to resolve this problem? How may I define that ‘homepage_url’ must redirect the user to my ‘board page’ or other?

    Thank very much in advance for your help…!!!


  • Logan Bailey

    Thank you David, that is a lot faster.

  • Logan Bailey

    add this line to your routes.rb file: root :to => ‘boards#show’, :as => ‘homepage’

    You should be able now to do “rake routes” and see
    homepage /(.:format) {:controller=>”boards”, :action=>”show”}

  • Logan Bailey

    the :as => should be in a string

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    It’s funny, you like it!

  • AshishFantwav

    Hey – I am definitely happy to find this. cool job!

  • guest

    I’m having trouble with the last step. confused with reply.html.erb and _reply_form.html.erb…