**Course Title:** Mastering Ruby on Rails: Building Scalable Web Applications **Section Title:** Real-Time Applications with ActionCable **Topic:** Introduction to real-time features in Rails with ActionCable **Introduction** In the previous topics, we have covered the basics of Ruby on Rails and its ecosystem. However, building scalable web applications often requires real-time features that enable instant updates and interactions between users. In this topic, we will explore how to introduce real-time features in Rails using ActionCable, a powerful library that enables bidirectional communication between the client and server. **What is ActionCable?** ActionCable is a Ruby on Rails library that provides a way to establish real-time communication between the client and server. It allows you to push updates from the server to connected clients, enabling features like live updates, chat applications, and live notifications. **Key Concepts** Before diving into ActionCable, let's cover some key concepts: * **Channel**: A channel is a connection between a client and a server. It represents a unidirectional communication channel. * **Cable**: A cable is a connection between multiple channels. It represents a bidirectional communication channel. * **Client**: A client is the application that connects to the server using ActionCable. * **Server**: The server is the application that provides the real-time features using ActionCable. **Setting up ActionCable** To set up ActionCable, you need to add the following gems to your Gemfile: ```ruby gem 'actioncable' ``` Then, run the following command to install the gem: ```bash bundle install ``` Next, create a new file `config/application.rb` and add the following code: ```ruby module YourApp class Application < Rails::Application config.action_cable.enabled = true end end ``` **Creating a Channel** To create a channel, you need to create a new file `app/channels/<channel_name>.rb`. For example, let's create a channel called `chat_channel`. ```ruby # app/channels/chat_channel.rb class ChatChannel < ApplicationCable::Channel def subscribed # This method is called when a client subscribes to the channel stream_from 'chat' end def unsubscribed # This method is called when a client unsubscribes from the channel end def speak(data) # This method is called when a client sends a message ActionCable.server.broadcast 'chat', message: data['message'] end end ``` **Creating a Client** To create a client, you need to create a new file `app/assets/javascripts/channels/chat_channel.js`. For example: ```javascript // app/assets/javascripts/channels/chat_channel.js import { Channel } from 'actioncable'; const chatChannel = new Channel('chat'); chatChannel.on('subscribe', () => { console.log('Client subscribed to the channel'); }); chatChannel.on('unsubscribe', () => { console.log('Client unsubscribed from the channel'); }); chatChannel.on('speak', (data) => { console.log(`Received message: ${data.message}`); }); chatChannel.join(); ``` **Broadcasting Messages** To broadcast messages to all connected clients, you need to use the `ActionCable.server.broadcast` method. For example: ```ruby # app/controllers/sessions_controller.rb class SessionsController < ApplicationController def create # Create a new user session session[:user_id] = params[:user_id] # Broadcast a message to all connected clients ActionCable.server.broadcast 'chat', message: 'Hello, world!' end end ``` **Conclusion** In this topic, we have introduced the basics of ActionCable and how to use it to build real-time features in Rails. We have covered key concepts, set up ActionCable, created a channel, created a client, and broadcasted messages to all connected clients. **Practical Takeaways** * Use ActionCable to establish real-time communication between the client and server. * Create channels to represent unidirectional communication channels. * Create clients to represent applications that connect to the server using ActionCable. * Use the `ActionCable.server.broadcast` method to broadcast messages to all connected clients. **Next Topic:** Building chat applications and live notifications. **Leave a comment or ask for help:** If you have any questions or need further clarification on any of the topics covered in this topic, please leave a comment below.