**Course Title:** Mastering Ruby on Rails: Building Scalable Web Applications **Section Title:** Real-Time Applications with ActionCable **Topic:** Build a real-time chat application using ActionCable for live messaging.(Lab topic) **Objective:** By the end of this topic, students will be able to design, develop, and deploy a real-time chat application using ActionCable, a Ruby on Rails gem that enables real-time communication between clients and servers. **Prerequisites:** Students should have a solid understanding of Ruby on Rails, including the topics covered in the previous sections. **Materials Needed:** * Ruby on Rails (latest version) * ActionCable (latest version) * A text editor or IDE (e.g., Visual Studio Code, Sublime Text) * A code editor (e.g., Atom, Brackets) * A terminal or command prompt **Step 1: Introduction to ActionCable** ActionCable is a Ruby on Rails gem that enables real-time communication between clients and servers. It provides a simple and efficient way to build real-time applications, such as live messaging, live updates, and collaborative editing. ActionCable uses WebSockets under the hood, which allow for bidirectional communication between the client and server. This enables real-time updates to be pushed to connected clients without requiring them to poll the server for updates. **Key Concepts:** * WebSockets * Real-time communication * ActionCable **Example:** ```ruby # app/channels/chat_channel.rb class ChatChannel < ApplicationCable::Channel def subscribed stream_from 'chat' end def unsubscribed # Any cleanup needed when channel is unsubscribed end def speak(data) ActionCable.server.broadcast 'chat', message: data['message'] end end ``` In this example, we define a `ChatChannel` that streams messages from the `chat` channel. When a message is sent, the `speak` method is called, which broadcasts the message to all connected clients. **Step 2: Setting up ActionCable** To use ActionCable, we need to add it to our Rails application. We can do this by running the following command: ```bash bundle add actioncable ``` Next, we need to configure ActionCable in our `config/application.rb` file: ```ruby module YourApp class Application < Rails::Application config.action_cable.enabled = true config.action_cable.default_url_options = { protocol: :ws } end end ``` **Step 3: Creating a Chat Application** To create a chat application, we need to create a new channel, a new controller, and a new view. We'll start by creating a new channel: ```ruby # app/channels/chat_channel.rb class ChatChannel < ApplicationCable::Channel def subscribed stream_from 'chat' end def unsubscribed # Any cleanup needed when channel is unsubscribed end def speak(data) ActionCable.server.broadcast 'chat', message: data['message'] end end ``` Next, we'll create a new controller: ```ruby # app/controllers/chat_controller.rb class ChatController < ApplicationController def index @messages = Message.all end def create @message = Message.new(message_params) @message.save ActionCable.server.broadcast 'chat', message: @message.message end private def message_params params.require(:message).permit(:message) end end ``` Finally, we'll create a new view: ```html <!-- app/views/chat/index.html.erb --> <h1>Chat</h1> <ul> <% @messages.each do |message| %> <li><%= message.message %></li> <% end %> </ul> <form action="/chat" method="post"> <input type="text" name="message" placeholder="Type a message..."> <button type="submit">Send</button> </form> ``` **Step 4: Testing the Chat Application** To test the chat application, we can use a tool like `curl` to send messages to the server: ```bash curl -X POST -H "Content-Type: application/json" -d '{"message": "Hello, world!"}' http://localhost:3000/chat ``` This should send a message to the server, which should then broadcast the message to all connected clients. **Conclusion:** In this topic, we've learned how to build a real-time chat application using ActionCable. We've covered the key concepts of WebSockets, real-time communication, and ActionCable, and we've created a simple chat application to demonstrate these concepts. **Practical Takeaways:** * Use ActionCable to build real-time applications * Understand the key concepts of WebSockets and real-time communication * Create a simple chat application using ActionCable **Additional Resources:** * ActionCable documentation: <https://github.com/rails/actioncable> * WebSockets documentation: <https://developer.mozilla.org/en-US/docs/WebSockets> **Leave a comment or ask for help:** If you have any questions or need further clarification on any of the concepts covered in this topic, please leave a comment below.