Ruby on Rails Basics Cheat Sheet

1. What is Ruby on Rails?

Ruby on Rails (RoR) is a web application framework written in Ruby. It follows the Model-View-Controller (MVC) architecture and promotes convention over configuration.

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2. Install Ruby on Rails

# Install Ruby
brew install ruby             # macOS
sudo apt install ruby-full    # Linux

# Install Rails
gem install rails

Verify Installation:

ruby -v
rails -v

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3. Create a New Rails Project

rails new myapp
cd myapp

Run the development server:

rails server

Visit http://localhost:3000 in your browser.

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4. Project Structure

myapp/
├── app/               # Application code (MVC)
│   ├── controllers/   # Controllers (Business logic)
│   ├── models/        # Models (Data and DB logic)
│   ├── views/         # Views (HTML, ERB templates)
├── config/            # Configuration files
├── db/                # Database schema and migrations
├── public/            # Static files
├── Gemfile            # Gem dependencies
└── Rakefile           # Task automation

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5. Generate Resources

Generate Model, Controller, and Views

rails generate scaffold Article title:string body:text

• Model: Defines the structure and relationships
• Controller: Manages requests and responses
• View: Renders HTML for users

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Apply Migrations

rails db:migrate

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6. MVC Structure

Model

app/models/article.rb

class Article < ApplicationRecord
    validates :title, presence: true
end

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Controller

app/controllers/articles_controller.rb

class ArticlesController < ApplicationController
  def index
    @articles = Article.all
  end

  def show
    @article = Article.find(params[:id])
  end
end

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View

app/views/articles/index.html.erb

<h1>Articles</h1>
<%= link_to 'New Article', new_article_path %>

<% @articles.each do |article| %>
  <h2><%= article.title %></h2>
  <p><%= article.body %></p>
  <%= link_to 'Show', article_path(article) %>
<% end %>

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7. Routing

config/routes.rb

Rails.application.routes.draw do
  resources :articles  # RESTful routes for articles
  root "articles#index"
end

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8. Create a Form

app/views/articles/_form.html.erb

<%= form_with(model: @article, local: true) do |form| %>
  <div>
    <%= form.label :title %>
    <%= form.text_field :title %>
  </div>

  <div>
    <%= form.label :body %>
    <%= form.text_area :body %>
  </div>

  <div>
    <%= form.submit %>
  </div>
<% end %>

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9. CRUD Operations

Create (New & Save)

@article = Article.new(article_params)
if @article.save
  redirect_to @article
else
  render :new
end

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Read (Index & Show)

@articles = Article.all
@article = Article.find(params[:id])

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Update

@article = Article.find(params[:id])
if @article.update(article_params)
  redirect_to @article
else
  render :edit
end

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Delete

@article.destroy
redirect_to articles_path

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10. Validations

app/models/article.rb

class Article < ApplicationRecord
  validates :title, presence: true
  validates :body, length: { minimum: 10 }
end

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11. Database Migrations

Create a Migration

rails generate migration AddPublishedToArticles published:boolean

db/migrate/xxxx_add_published_to_articles.rb

class AddPublishedToArticles < ActiveRecord::Migration[6.1]
  def change
    add_column :articles, :published, :boolean, default: false
  end
end

Apply migration:

rails db:migrate

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12. Associations

One-to-Many

Article has many comments.

class Article < ApplicationRecord
  has_many :comments
end

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Comment belongs to an article.

class Comment < ApplicationRecord
  belongs_to :article
end

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13. Partials

app/views/articles/_article.html.erb

<h2><%= article.title %></h2>
<p><%= article.body %></p>

Render in views:

<%= render @articles %>

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14. Flash Messages

flash[:notice] = "Article was successfully created"
flash[:alert] = "Something went wrong"

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15. Debugging

<%= debug(params) %>

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16. Testing

Generate Tests

rails generate test_unit:scaffold Article

Run Tests

rails test

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17. Rails Console

rails console

Article.all
Article.create(title: "Rails Guide")

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18. Seed Database

db/seeds.rb

Article.create(title: "First Article", body: "This is the body")

Run seeds:

rails db:seed

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19. API with Rails

# config/routes.rb
namespace :api do
  resources :articles
end

app/controllers/api/articles_controller.rb

class Api::ArticlesController < ApplicationController
  def index
    render json: Article.all
  end
end

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20. Useful Commands

rails routes             # List all routes
rails dbconsole          # Connect to DB
rails generate model     # Create a model
rails generate scaffold  # Create CRUD resources
rails destroy scaffold   # Rollback
rails db:rollback        # Undo last migration