Ruby on Rails Reference & Cheatsheet

rails new myapp -d postgresql           # New app with PostgreSQL
rails generate scaffold Product name:string price:decimal
rails generate migration AddStockToProducts stock:integer
rails db:create db:migrate               # Create DB + run migrations
rails server                              # Start dev server (localhost:3000)
rails console                             # Interactive Rails console

# config/routes.rb
Rails.application.routes.draw do
  resources :products do
    collection do
      get :search          # GET /products/search
    end
    member do
      post :publish        # POST /products/:id/publish
    end
    resources :reviews, only: [:create, :destroy]
  end

  namespace :admin do
    resources :users       # GET /admin/users, etc.
  end
end

# Model with validations and associations
class Product < ApplicationRecord
  belongs_to :category
  has_many :reviews, dependent: :destroy

  validates :name, presence: true, length: { maximum: 100 }
  validates :price, numericality: { greater_than: 0 }
  validates :sku, uniqueness: true

  scope :available, -> { where("stock_count > 0") }
  scope :by_price, -> { order(price: :asc) }
end

# Query examples
Product.available
Product.where("price > ?", 10)
Product.order(created_at: :desc).limit(5)
Product.joins(:category).where(categories: { name: "Electronics" })

class ProductsController < ApplicationController
  before_action :set_product, only: [:show, :edit, :update, :destroy]

  def index
    @products = Product.all
    respond_to do |format|
      format.html
      format.json { render json: @products }
    end
  end

  def create
    @product = Product.new(product_params)
    if @product.save
      redirect_to @product, notice: "Product created."
    else
      render :new, status: :unprocessable_entity
    end
  end

  private

  def set_product
    @product = Product.find(params[:id])
  end

  def product_params
    params.require(:product).permit(:name, :price, :description)
  end
end

<%# app/views/products/index.html.erb %>
<h1>Products</h1>
<%= link_to "New Product", new_product_path, class: "btn" %>

<table>
  <thead>
    <tr><th>Name</th><th>Price</th><th>Actions</th></tr>
  </thead>
  <tbody>
    <% @products.each do |product| %>
      <tr>
        <td><%= product.name %></td>
        <td><%= number_to_currency(product.price) %></td>
        <td>
          <%= link_to "Show", product %>
          <%= link_to "Edit", edit_product_path(product) %>
          <%= button_to "Delete", product, method: :delete %>
        </td>
      </tr>
    <% end %>
  </tbody>
</table>

# Gemfile
gem "devise"

# Terminal
rails generate devise:install
rails generate devise User
rails db:migrate

# Controller
before_action :authenticate_user!

# View helpers
user_signed_in?
current_user
user_session

add_column :table, :column, :type
remove_column :table, :column
rename_column :table, :old, :new
add_index :table, :column
add_reference :table, :other, foreign_key: true
create_join_table :table1, :table2