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# Install Rails
gem install rails

# Create a new Rails project
rails new project_name

# Create a new Rails project with specific options
rails new project_name \
  -d postgresql \
  --skip-test \
  --webpack=react

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# Using RVM
rvm install 3.1.0
rvm use 3.1.0

# Using rbenv
rbenv install 3.1.0
rbenv global 3.1.0

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# config/routes.rb
Rails.application.routes.draw do
  # RESTful routes for a resource
  resources :users

  # Custom routes
  get '/about', to: 'pages#about'
  
  # Nested routes
  resources :posts do
    resources :comments
  end

  # Namespaced routes
  namespace :admin do
    resources :users
  end
}

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# Generated route helpers
users_path        # => '/users'
new_user_path     # => '/users/new'
edit_user_path(user) # => '/users/1/edit'

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class UsersController < ApplicationController
  # Filter/before action
  before_action :set_user, only: [:show, :edit, :update, :destroy]

  def index
    @users = User.all
  end

  def show
  end

  def new
    @user = User.new
  end

  def create
    @user = User.new(user_params)
    if @user.save
      redirect_to @user, notice: 'User created!'
    else
      render :new
    end
  end

  private

  def set_user
    @user = User.find(params[:id])
  end

  def user_params
    params.require(:user).permit(:name, :email)
  end
end

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def user_params
  params.require(:user).permit(
    :name, 
    :email, 
    addresses: [:street, :city]
  )
end

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<%# Embedded Ruby (ERB) %>
<h1>Welcome, <%= @user.name %></h1>

<%# Conditional %>
<% if @users.any? %>
  <ul>
    <% @users.each do |user| %>
      <li><%= user.name %></li>
    <% end %>
  </ul>
<% end %>

<%# Partials %>
<%= render 'shared/header' %>
<%= render partial: 'user', collection: @users %>

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# In view or helper
link_to 'Edit', edit_user_path(user)
image_tag 'logo.png'
number_to_currency(price)

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class User < ApplicationRecord
  # Validations
  validates :email, 
            presence: true, 
            uniqueness: true,
            format: { with: /\A[\w+\-.]+@[a-z\d\-]+(\.[a-z\d\-]+)*\.[a-z]+\z/i }
  
  # Associations
  has_many :posts
  belongs_to :organization, optional: true

  # Scopes
  scope :active, -> { where(active: true) }
  scope :recent, ->(days) { where('created_at >= ?', days.days.ago) }

  # Class method
  def self.find_by_email(email)
    find_by(email: email)
  end

  # Instance method
  def full_name
    "#{first_name} #{last_name}"
  end
end

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# Finding records
User.find(1)                  # Find by ID
User.find_by(email: 'x@y.com')# Find first matching record
User.where(active: true)      # Find all matching records
User.order(created_at: :desc) # Ordered results
User.limit(10)                # Limit results
User.includes(:posts)         # Eager loading

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# Generate migration
rails generate migration CreateUsers name:string email:string

# Run migrations
rails db:migrate
rails db:rollback
rails db:reset

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# Migration example
class CreateUsers < ActiveRecord::Migration[6.1]
  def change
    create_table :users do |t|
      t.string :name
      t.string :email, index: { unique: true }
      t.timestamps
    end
  end
end

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# db/seeds.rb
5.times do
  User.create!(
    name: Faker::Name.name,
    email: Faker::Internet.email
  )
end

rails db:seed

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# Gemfile
gem 'devise'

# Generate configuration
rails generate devise:install
rails generate devise User

# In application controller
before_action :authenticate_user!

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# Gemfile
gem 'pundit'

# Generate policy
rails generate pundit:policy User

# Example policy
class UserPolicy < ApplicationPolicy
  def update?
    user.admin? || record == user
  end
end

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# Gemfile
group :development, :test do
  gem 'rspec-rails'
end

# Generate specs
rails generate rspec:install

# Model spec example
RSpec.describe User, type: :model do
  it "is valid with valid attributes" do
    user = User.new(name: "John", email: "john@example.com")
    expect(user).to be_valid
  end
end

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# Rails Commands
rails new project_name
rails server        # Start server
rails console      # Interactive console
rails generate     # Generate models, controllers
rails destroy      # Remove generated resources
rails routes       # List routes
rails dbconsole    # Database console

# Bundler
bundle install     # Install dependencies
bundle update      # Update gems

# Testing
rails test
rspec              # For RSpec

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# config/environments/development.rb
Rails.application.configure do
  config.cache_classes = false
  config.active_record.verbose_query_logs = true
end

# config/application.rb
module MyApp
  class Application < Rails::Application
    config.time_zone = 'Eastern Time (US & Canada)'
    config.generators do |g|
      g.test_framework :rspec
    end
  end
end

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# Debugging
binding.pry        # Breakpoint with Pry
Rails.logger.debug # Logging

# Common Issues
# - N+1 queries: Use includes, eager loading
# - Slow queries: Use database indexes
# - Memory leaks: Profile with tools like rack-mini-profiler