**Course Title:** Mastering Ruby on Rails: Building Scalable Web Applications **Section Title:** RESTful API Development with Rails **Topic:** Creating APIs using Rails controllers **Introduction** In the previous topic, we covered the basics of RESTful API development with Rails. In this topic, we will dive deeper into creating APIs using Rails controllers. We will explore how to handle JSON requests and responses, and how to use Rails' built-in features to create robust and scalable APIs. **What is an API?** Before we begin, let's define what an API is. An API, or Application Programming Interface, is a set of defined rules that enables different applications, services, or systems to communicate with each other. In the context of Rails, an API is a set of endpoints that expose data and functionality to external applications. **Creating APIs using Rails controllers** To create an API using Rails controllers, we need to follow these steps: 1. **Define your API endpoints**: In your Rails application, define the API endpoints that you want to expose. These endpoints should be RESTful, meaning they should follow the standard HTTP methods (GET, POST, PUT, DELETE, etc.). 2. **Create a controller**: Create a new controller that will handle the API requests. This controller should inherit from `ApplicationController` and use the `api_only` method to specify that it should only handle API requests. 3. **Define the API actions**: In the controller, define the API actions that will handle the requests. These actions should use the `respond_to` method to specify the format of the response. 4. **Use the `respond_to` method**: The `respond_to` method is used to specify the format of the response. In this case, we want to respond with JSON, so we use the `json` method. **Example Code** Here is an example of how to create an API using Rails controllers: ```ruby # app/controllers/api/users_controller.rb class Api::UsersController < ApplicationController def index users = User.all respond_to do |format| format.json { render json: users } end end def show user = User.find(params[:id]) respond_to do |format| format.json { render json: user } end end end ``` **Handling JSON requests and responses** To handle JSON requests and responses, we use the `respond_to` method and the `json` method. The `respond_to` method specifies the format of the response, and the `json` method renders the response as JSON. **Example Code** Here is an example of how to handle JSON requests and responses: ```ruby # app/controllers/api/users_controller.rb class Api::UsersController < ApplicationController def index users = User.all respond_to do |format| format.json { render json: users } end end def show user = User.find(params[:id]) respond_to do |format| format.json { render json: user } end end end ``` **Practical Takeaways** * To create an API using Rails controllers, define your API endpoints, create a controller, define the API actions, and use the `respond_to` method to specify the format of the response. * To handle JSON requests and responses, use the `respond_to` method and the `json` method. * Use the `api_only` method to specify that a controller should only handle API requests. **Additional Resources** * Rails API Documentation: <https://guides.rubyonrails.org/api_versions.html> * Rails API Tutorial: <https://guides.rubyonrails.org/api_versions.html> **Leave a comment or ask for help** If you have any questions or need further clarification on this topic, please leave a comment below. I'll be happy to help!