Steps

Step 1: Add a new controller action for voting

Edit app/controllers/topics_controller.rb and add this method at the end of the controller, above the private keyword:

def upvote
  @topic = Topic.find(params[:id])
  @topic.votes.create
  redirect_to(topics_path)
end

• @topic = Topic.find(params[:id]) finds the topic in the database with that id and stores it in the variable @topic.
• @topic.votes.create creates a new vote for the current topic and saves it in the database.
• redirect_to(topics_path) tells the browser to go back to topics_path (the topics list).

Step 2: Add a new route for voting

Open config/routes.rb and find the section that looks like this:

resources :topics

Replace that line so it looks like this:

resources :topics do
  member do
    post 'upvote'
  end
end

Verify that upvote route was added successfully by checking the output of rails routes or http://localhost:3000/rails/info. You should see a line that looks like this:

      Prefix Verb   URI Pattern                  Controller#Action
upvote_topic POST   /topics/:id/upvote(.:format) topics#upvote

Step 3: Add the button to the view

Edit app/views/topics/index.html.erb so that the bottom loop looks like this:

<% @topics.each do |topic| %>
  <tr>
    <td><%= topic.title %></td>
    <td><%= topic.description %></td>
    <td><%= pluralize(topic.votes.count, "vote") %></td>
    <td><%= button_to '+1', upvote_topic_path(topic), method: :post %></td>
    <td><%= link_to 'Show', topic %></td>
    <td><%= link_to 'Edit', edit_topic_path(topic) %></td>
    <td><%= link_to 'Destroy', topic, method: :delete, data: { confirm: 'Are you sure?' } %></td>
  </tr>
<% end %>

• pluralize(topic.votes.count, "vote") displays the number of votes the topic has, plus the word "vote" or "votes" accordingly.
• button_to '+1' creates an HTML button with the text "+1".
• upvote_topic_path(topic) creates the appropriate URL for the action we want to invoke. In this case, we want to upvote the current topic.
  • upvote_topic_path(topic) would return /topics/42/upvote (if topic.id was 42)
• method: :post ensures we do the create action of CRUD, not the read action.

Step 4: Confirm your changes in the browser

Go back to http://localhost:3000/topics and play.

Revel in the fact that you didn't have to restart the server to see these changes. Hawt, no?