**Course Title:** Ruby Programming: From Basics to Advanced Techniques **Section Title:** Introduction to Ruby on Rails **Topic:** Build a basic Ruby on Rails application with simple CRUD functionality. (Lab topic) **Overview** In this lab exercise, we will build a basic Ruby on Rails application with simple CRUD (Create, Read, Update, Delete) functionality. This exercise is designed to give you hands-on experience with Rails and help you understand how to create a fully functional web application. **Prerequisites** Before starting this lab, make sure you have: 1. Installed Ruby and Rails on your system (refer to the [Rails installation guide](https://guides.rubyonrails.org/v6.1/getting_started.html) if you haven't already). 2. Set up aRails development environment. 3. Familiarity with the basics of Rails (MVC architecture, routing, etc.). **Step 1: Create a new Rails application** Open a terminal and run the following command to create a new Rails application: ```bash rails new crud_app ``` This will create a new Rails application called `crud_app`. **Step 2: Configure the database** In this lab, we will use SQLite as our database. Open the `config/database.yml` file and make sure it looks like this: ```yml default: &default adapter: sqlite3 pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %> timeout: 5000 development: <<: *default database: db/development.sqlite3 test: <<: *default database: db/test.sqlite3 ``` **Step 3: Create a model** In Rails, a model represents a database table. Let's create a `Book` model: ```bash rails generate model Book title:string author:string ``` This will create a `book.rb` file in the `app/models` directory and a `books` table in the database. **Step 4: Run the migration** To create the `books` table in the database, run the following command: ```bash rails db:migrate ``` **Step 5: Create a controller** A controller handles HTTP requests and sends responses. Let's create a `BooksController`: ```bash rails generate controller Books ``` This will create a `books_controller.rb` file in the `app/controllers` directory. **Step 6: Define CRUD actions** In the `books_controller.rb` file, add the following methods: ```ruby class BooksController < ApplicationController def index @books = Book.all end def show @book = Book.find(params[:id]) end def new @book = Book.new end def create @book = Book.new(book_params) if @book.save redirect_to books_path else render :new end end def edit @book = Book.find(params[:id]) end def update @book = Book.find(params[:id]) if @book.update(book_params) redirect_to books_path else render :edit end end def destroy @book = Book.find(params[:id]) @book.destroy redirect_to books_path end private def book_params params.require(:book).permit(:title, :author) end end ``` These methods handle the CRUD operations: * `index`: lists all books * `show`: shows a single book * `new`: creates a new book * `create`: saves a new book * `edit`: edits an existing book * `update`: updates an existing book * `destroy`: deletes a book **Step 7: Add routes** In the `config/routes.rb` file, add the following routes: ```ruby Rails.application.routes.draw do resources :books end ``` This will create the following routes: * `GET /books`: lists all books * `GET /books/:id`: shows a single book * `GET /books/new`: creates a new book * `POST /books`: saves a new book * `GET /books/:id/edit`: edits an existing book * `PATCH /books/:id`: updates an existing book * `DELETE /books/:id`: deletes a book **Step 8: Create views** Create the following views: * `index.html.erb`: lists all books * `show.html.erb`: shows a single book * `new.html.erb`: creates a new book * `edit.html.erb`: edits an existing book You can use the following code as a starting point: ```erb <!-- app/views/books/index.html.erb --> <h1>Books</h1> <ul> <% @books.each do |book| %> <li> <%= link_to book.title, book_path(book) %> </li> <% end %> </ul> <!-- app/views/books/show.html.erb --> <h1><%= @book.title %></h1> <p>Author: <%= @book.author %></p> <!-- app/views/books/new.html.erb --> <h1>New Book</h1> <%= form_for(@book) do |form| %> <%= form.label :title %> <%= form.text_field :title %> <%= form.label :author %> <%= form.text_field :author %> <%= form.submit %> <% end %> <!-- app/views/books/edit.html.erb --> <h1>Edit Book</h1> <%= form_for(@book) do |form| %> <%= form.label :title %> <%= form.text_field :title %> <%= form.label :author %> <%= form.text_field :author %> <%= form.submit %> <% end %> ``` **Conclusion** In this lab, we created a basic Ruby on Rails application with simple CRUD functionality. We defined a `Book` model, created a `BooksController` with CRUD actions, added routes, and created views to display and edit books. **What's next?** In the next topic, we will explore the routing system in Rails and learn how to create custom routes and actions. **Questions or comments?** If you have any questions or comments about this lab, please leave them below. External resources: * [Rails Guide: Getting Started](https://guides.rubyonrails.org/v6.1/getting_started.html) * [Rails Guide: Active Record](https://guides.rubyonrails.org/v6.1/active_record_basics.html) * [Rails Guide: ActionController](https://guides.rubyonrails.org/v6.1/action_controller_overview.html) * [Rails Guide: Routing](https://guides.rubyonrails.org/v6.1/routing.html)