The Ultimate Ruby on Rails Cheatsheet

# ── Rails Routing ──
Rails.application.routes.draw do
  # Root route
  root 'articles#index'

  # Resource routing (RESTful)
  resources :articles do
    member do
      post :publish    # POST /articles/:id/publish
      delete :archive  # DELETE /articles/:id/archive
    end
    collection do
      get :drafts      # GET /articles/drafts
      get :search      # GET /articles/search
    end
    resources :comments, only: [:create, :destroy]
    resources :likes, shallow: true
  end

  # Nested resources
  resources :users do
    resources :posts, shallow: true
  end

  # Singular resource
  resource :profile, only: [:show, :edit, :update]

  # Custom routes
  get 'about', to: 'pages#about', as: :about
  get 'login', to: 'sessions#new', as: :login
  post 'login', to: 'sessions#create'
  delete 'logout', to: 'sessions#destroy', as: :logout

  # Namespace
  namespace :admin do
    resources :users, :articles, :settings
  end

  # Scope with module
  scope '/api', module: :api do
    resources :articles, defaults: { format: :json }
  end
end

# ── Controller (MVC) ──
class ArticlesController < ApplicationController
  before_action :set_article, only: [:show, :edit, :update, :destroy]
  before_action :authenticate_user!, except: [:index, :show]

  # GET /articles
  def index
    @articles = Article.includes(:author, :tags)
                     .published
                     .order(created_at: :desc)
                     .page(params[:page])
                     .per(10)
  end

  # GET /articles/:id
  def show
    @comment = @article.comments.build
    increment_view_count
  end

  # GET /articles/new
  def new
    @article = current_user.articles.build
  end

  # POST /articles
  def create
    @article = current_user.articles.build(article_params)
    if @article.save
      redirect_to @article, notice: 'Article was successfully created.'
    else
      render :new, status: :unprocessable_entity
    end
  end

  # PATCH/PUT /articles/:id
  def update
    if @article.update(article_params)
      redirect_to @article, notice: 'Article was successfully updated.'
    else
      render :edit, status: :unprocessable_entity
    end
  end

  # DELETE /articles/:id
  def destroy
    @article.destroy
    redirect_to articles_url, notice: 'Article was successfully deleted.'
  end

  private

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

  def article_params
    params.require(:article).permit(:title, :body, :status, :category_id, tag_ids: [])
  end

  def increment_view_count
    @article.increment!(:view_count)
  end
end

# ── Model Definition ──
class Article < ApplicationRecord
  belongs_to :author, class_name: 'User', inverse_of: :articles
  belongs_to :category, optional: true
  has_many :comments, dependent: :destroy
  has_many :likes, as: :likeable, dependent: :destroy
  has_and_belongs_to_many :tags
  has_one_attached :cover_image
  has_many_attached :gallery_images

  enum status: { draft: 0, published: 1, archived: 2 }

  # Validations
  validates :title, presence: true, length: { minimum: 5, maximum: 200 }
  validates :body, presence: true, length: { minimum: 20 }
  validates :status, inclusion: { in: statuses.keys }
  validates :title, uniqueness: { scope: :author_id, case_sensitive: false }
  validates :cover_image, content_type: ['image/png', 'image/jpeg'],
            size: { less_than: 5.megabytes }

  # Scopes
  scope :published, -> { where(status: :published) }
  scope :recent, -> { order(created_at: :desc) }
  scope :by_category, ->(slug) { joins(:category).where(categories: { slug: slug }) }
  scope :search, ->(query) {
    where('title ILIKE ? OR body ILIKE ?', "%query%", "%query%")
  }

  # Callbacks
  before_validation :generate_slug, on: :create
  after_create :send_notification
  after_update :clear_cache, if: :saved_change_to_status?

  # Instance methods
  def reading_time
    (body.split.size / 200.0).ceil
  end

  def truncated_body(length = 150)
    body.truncate(length)
  end

  private

  def generate_slug
    self.slug = title.parameterize if slug.blank?
  end

  def send_notification
    NotificationMailer.new_article(self).deliver_later
  end

  def clear_cache
    Rails.cache.delete("article-#{id}")
  end
end

# ── ActiveRecord Queries ──
# Basic queries
Article.all
Article.first
Article.last
Article.find(1)
Article.find_by(slug: 'hello-world')
Article.find_or_create_by(title: 'Default', body: '...')
Article.find_or_initialize_by(title: 'Default')

# Where clauses
Article.where(status: :published)
Article.where('view_count > ?', 100)
Article.where(created_at: 1.week.ago..Time.current)
Article.where.not(status: :draft)
Article.where(status: [:published, :archived])

# Ordering, limiting, offset
Article.order(:created_at)
Article.order(created_at: :desc, title: :asc)
Article.limit(10).offset(20)

# Joins & includes
Article.joins(:comments).group('articles.id').having('COUNT(comments.id) > 5')
Article.includes(:author, :comments).first  # Eager loading
Article.eager_load(:author)  # Always uses LEFT OUTER JOIN
Article.preload(:tags)       # Separate queries

# Pluck & select
Article.pluck(:title, :status)
Article.select(:id, :title).map(&:title)

# Calculations
Article.count
Article.average(:view_count)
Article.minimum(:created_at)
Article.maximum(:view_count)
Article.sum(:view_count)
Article.group(:status).count
Article.group(:category_id).average(:view_count)

# Updating & deleting
article.update(title: 'New Title')
Article.where(status: :draft).update_all(status: :published)
Article.where('created_at < ?', 1.year.ago).delete_all

# ── Migration Commands ──
rails generate model Article title:string body:text status:integer user:references
rails generate migration AddSlugToArticles slug:string:uniq
rails generate migration CreateJoinTableUserRole user role
rails db:create              # Create database
rails db:migrate             # Run pending migrations
rails db:rollback            # Undo last migration
rails db:rollback STEP=3     # Undo last 3 migrations
rails db:migrate:status      # Show migration status
rails db:seed                # Run db/seeds.rb
rails db:drop                # Drop the database
rails db:reset               # Drop + create + migrate + seed
rails db:prepare             # Create, migrate, and seed if needed

# ── Migration Examples ──
class CreateArticles < ActiveRecord::Migration[7.1]
  def change
    create_table :articles do |t|
      t.string :title, null: false, limit: 200
      t.text :body, null: false
      t.string :slug
      t.integer :status, null: false, default: 0
      t.references :author, foreign_key: { to_table: :users }, null: false
      t.references :category, foreign_key: true
      t.integer :view_count, null: false, default: 0

      t.timestamps
    end

    add_index :articles, :slug, unique: true
    add_index :articles, :status
    add_index :articles, [:author_id, :status]
    add_index :articles, :created_at
  end
end

class AddPublishedAtToArticles < ActiveRecord::Migration[7.1]
  def change
    add_column :articles, :published_at, :datetime
    add_column :articles, :excerpt, :text

    reversible do |dir|
      dir.up do
        Article.where(status: :published).find_each do |article|
          article.update_column(:published_at, article.created_at)
        end
      end
    end
  end
end

<!-- ── View Template ── -->
<% content_for :title, 'Articles' %>

<div class="container">
  <% if notice %>
    <div class="alert alert-info"><%= notice %></div>
  <% end %>

  <div class="header">
    <h1>Articles</h1>
    <%= link_to 'New Article', new_article_path, class: 'btn btn-primary' %>
  </div>

  <!-- Pagination -->
  <%= paginate @articles %>

  <% @articles.each do |article| %>
    <article class="card">
      <h2><%= link_to article.title, article %></h2>
      <div class="meta">
        <span>By <%= article.author.name %></span>
        <span><%= time_ago_in_words(article.created_at) %> ago</span>
        <span><%= pluralize(article.view_count, 'view') %></span>
        <span class="badge"><%= article.status %></span>
      </div>
      <p><%= truncate(article.body, length: 200) %></p>
      <div class="tags">
        <% article.tags.each do |tag| %>
          <span class="tag"><%= tag.name %></span>
        <% end %>
      </div>
    </article>
  <% end %>

  <%= paginate @articles %>
</div>

<!-- ── Partial with locals ── -->
<%# Render: render 'shared/article_card', article: @article %>
<div class="article-card <%= article.status %>">
  <% if article.cover_image.attached? %>
    <%= image_tag article.cover_image, class: 'cover' %>
  <% end %>

  <div class="content">
    <h3><%= link_to article.title, article_path(article) %></h3>
    <p class="meta">
      by <%= article.author.name %> &middot;
      <%= l(article.created_at, format: :short) %>
    </p>
    <p><%= article.truncated_body %></p>

    <div class="actions">
      <%= link_to 'Read more', article, class: 'btn btn-sm' %>
      <% if policy(article).edit? %>
        <%= link_to 'Edit', edit_article_path(article), class: 'btn btn-sm btn-outline' %>
      <% end %>
    </div>
  </div>
</div>

# ── Essential Gems ──
source 'https://rubygems.org'
ruby '3.3.0'

gem 'rails', '~> 7.1.0'
gem 'pg', '~> 1.5'                    # PostgreSQL adapter
gem 'puma', '~> 6.0'                  # App server
gem 'devise', '~> 4.9'                # Authentication
gem 'pundit', '~> 2.3'                # Authorization
gem 'friendly_id', '~> 5.5'           # Slugs
gem 'kaminari', '~> 1.2'              # Pagination
gem 'active_storage_validations'       # File validations
gem 'mini_magick', '~> 4.12'          # Image processing
gem 'image_processing', '~> 1.2'      # Variant support
gem 'sidekiq', '~> 7.0'               # Background jobs
gem 'redis', '~> 5.0'                 # Redis client
gem 'bootsnap', require: false         # Faster boot
gem 'turbo-rails'                      # Hotwire Turbo
gem 'stimulus-rails'                   # Hotwire Stimulus
gem 'tailwindcss-rails'                # Tailwind CSS

group :development, :test do
  gem 'rspec-rails', '~> 6.0'
  gem 'factory_bot_rails'
  gem 'faker'
  gem 'pry-rails'
  gem 'rubocop-rails', require: false
  gem 'bullet'                         # N+1 detection
end

group :development do
  gem 'web-console'
  gem 'spring'
end

group :test do
  gem 'shoulda-matchers', '~> 5.0'
  gem 'capybara', '~> 3.39'
  gem 'selenium-webdriver'
  gem 'database_cleaner-active_record'
end

# ── RSpec Tests ──
require 'rails_helper'

RSpec.describe Article, type: :model do
  describe 'Validations' do
    it { should validate_presence_of(:title) }
    it { should validate_length_of(:title).is_at_least(5) }
    it { should validate_presence_of(:body) }
    it { should validate_length_of(:body).is_at_least(20) }
    it { should validate_inclusion_of(:status).in_array(%w[draft published archived]) }
    it { should belong_to(:author).class_name('User') }
    it { should have_many(:comments).dependent(:destroy) }
    it { should have_and_belong_to_many(:tags) }
  end

  describe 'Scopes' do
    let!(:published) { create_list(:article, 3, status: :published) }
    let!(:draft) { create(:article, status: :draft) }

    it 'returns only published articles' do
      expect(Article.published).to eq(published)
    end
  end

  describe '#reading_time' do
    it 'calculates reading time based on word count' do
      article = create(:article, body: 'Word ' * 400)
      expect(article.reading_time).to eq(2)
    end
  end

  describe 'Callbacks' do
    it 'generates slug before validation on create' do
      article = create(:article, title: 'My First Article')
      expect(article.slug).to eq('my-first-article')
    end
  end
end