### Install Guides Dependencies and Generate HTML

Source: https://guides.rubyonrails.org/v7.0/contributing_to_ruby_on_rails.html

Installs necessary gems for generating HTML guides and then generates the HTML guides for a specific language. Use `bundle config --delete without` to undo.

```bash
# only install gems necessary for the guides. To undo run: bundle config --delete without
$ bundle install --without job cable storage ujs test db
$ cd guides/
$ bundle exec rake guides:generate:html GUIDES_LANGUAGE=it-IT

```

--------------------------------

### Generate All HTML Guides

Source: https://guides.rubyonrails.org/v7.0/ruby_on_rails_guides_guidelines.html

Command to generate all HTML guides. Ensure you are in the 'guides' directory and have Bundler installed.

```bash
$ bundle exec rake guides:generate
```

```bash
$ bundle exec rake guides:generate:html
```

--------------------------------

### Rails::Server#start Method

Source: https://guides.rubyonrails.org/v7.0/initialization.html

Defines the startup behavior for the Rails server, including signal trapping, directory creation, and development caching setup.

```Ruby
module Rails
  class Server < ::Rack::Server
    def start(after_stop_callback = nil)
      trap(:INT) { exit }
      create_tmp_directories
      setup_dev_caching
      log_to_stdout if options[:log_stdout]

      super()
      # ...
    end

    private
      def setup_dev_caching
        if options[:environment] == "development"
          Rails::DevCaching.enable_by_argument(options[:caching])
        end
      end

      def create_tmp_directories
        %w(cache pids sockets).each do |dir_to_make|
          FileUtils.mkdir_p(File.join(Rails.root, "tmp", dir_to_make))
        end
      end

      def log_to_stdout
        wrapped_app # touch the app so the logger is set up

        console = ActiveSupport::Logger.new(STDOUT)
        console.formatter = Rails.logger.formatter
        console.level = Rails.logger.level

        unless ActiveSupport::Logger.logger_outputs_to?(Rails.logger, STDOUT)
          Rails.logger.extend(ActiveSupport::Logger.broadcast(console))
        end
      end
  end
end

```

--------------------------------

### List Available Homebrew Services on macOS

Source: https://guides.rubyonrails.org/v7.0/development_dependencies_install.html

After installing services with Homebrew, use this command to list all services that can be managed. This helps in identifying services to start.

```bash
$ brew services list

```

--------------------------------

### Start Standalone Cable Server

Source: https://guides.rubyonrails.org/v7.0/action_cable_overview.html

Use a binstub to start the standalone Action Cable server on a specific port.

```bash
#!/bin/bash
bundle exec puma -p 28080 cable/config.ru

```

--------------------------------

### Start a Specific Homebrew Service on macOS

Source: https://guides.rubyonrails.org/v7.0/development_dependencies_install.html

Replace 'mysql' with the name of the service you wish to start. This command is used to manually start individual services installed via Homebrew.

```bash
$ brew services start mysql

```

--------------------------------

### Install All Dependencies with Homebrew on macOS

Source: https://guides.rubyonrails.org/v7.0/development_dependencies_install.html

Use this command to install all required services and tools using Homebrew's bundle feature. Ensure Homebrew is installed first.

```bash
$ brew bundle

```

--------------------------------

### PostgreSQL EXPLAIN output example

Source: https://guides.rubyonrails.org/v7.0/active_record_querying.html

This is an example of the `EXPLAIN` output for a query executed on a PostgreSQL database.

```text
EXPLAIN for: SELECT "customers".* FROM "customers" INNER JOIN "orders" ON "orders"."customer_id" = "customers"."id" WHERE "customers"."id" = $1 [["id", 1]]
                                  QUERY PLAN
------------------------------------------------------------------------------
 Nested Loop  (cost=4.33..20.85 rows=4 width=164)
    ->  Index Scan using customers_pkey on customers  (cost=0.15..8.17 rows=1 width=164)
          Index Cond: (id = '1'::bigint)
    ->  Bitmap Heap Scan on orders  (cost=4.18..12.64 rows=4 width=8)
          Recheck Cond: (customer_id = '1'::bigint)
          ->  Bitmap Index Scan on index_orders_on_customer_id  (cost=0.00..4.18 rows=4 width=0)
                Index Cond: (customer_id = '1'::bigint)
(7 rows)
```

--------------------------------

### Generate Specific HTML Guide

Source: https://guides.rubyonrails.org/v7.0/ruby_on_rails_guides_guidelines.html

Command to generate only a specific Markdown guide file. This is useful for testing changes to a single guide.

```bash
$ touch my_guide.md
$ bundle exec rake guides:generate ONLY=my_guide
```

--------------------------------

### MySQL/MariaDB EXPLAIN output example

Source: https://guides.rubyonrails.org/v7.0/active_record_querying.html

This is an example of the `EXPLAIN` output for a query executed on a MySQL or MariaDB database.

```text
EXPLAIN for: SELECT `customers`.* FROM `customers` INNER JOIN `orders` ON `orders`.`customer_id` = `customers`.`id` WHERE `customers`.`id` = 1
+----+-------------+------------+-------+---------------+---------+---------+-------+------+-------------+
| id | select_type | table      | type  | possible_keys | key     | key_len | ref   | rows | Extra       |
+----+-------------+------------+-------+---------------+---------+---------+-------+------+-------------+
|  1 | SIMPLE      | customers  | const | PRIMARY       | PRIMARY | 4       | const |    1 |             |
|  1 | SIMPLE      | orders     | ALL   | NULL          | NULL    | NULL    | NULL  |    1 | Using where |
+----+-------------+------------+-------+---------------+---------+---------+-------+------+-------------+

2 rows in set (0.00 sec)
```

--------------------------------

### Install All Dependencies on Arch Linux

Source: https://guides.rubyonrails.org/v7.0/development_dependencies_install.html

Installs required packages for Ruby on Rails development on Arch Linux using pacman. Includes MariaDB (as MySQL is not supported), PostgreSQL, Redis, Memcached, and multimedia tools. Also initializes and starts services.

```bash
$ sudo pacman -S sqlite mariadb libmariadbclient mariadb-clients postgresql postgresql-libs redis memcached imagemagick ffmpeg mupdf mupdf-tools poppler yarn libxml2
$ sudo mariadb-install-db --user=mysql --basedir=/usr --datadir=/var/lib/mysql
$ sudo systemctl start redis mariadb memcached

```

--------------------------------

### Interactive Example for Create and Update Callbacks

Source: https://guides.rubyonrails.org/v7.0/active_record_callbacks.html

This interactive example shows the output when creating and updating a User record using the defined `after_create_commit` and `after_update_commit` callbacks.

```irb
irb> @user = User.create # prints nothing

irb> @user.save # updating @user
User was saved to database
```

--------------------------------

### Install Action Mailbox Migrations and Migrate Database

Source: https://guides.rubyonrails.org/v7.0/action_mailbox_basics.html

Install the necessary migrations for InboundEmail records and ensure your database is up-to-date.

```bash
$ bin/rails action_mailbox:install
$ bin/rails db:migrate

```

--------------------------------

### Fragment Cache Logging Example (Verbose)

Source: https://guides.rubyonrails.org/v7.0/configuring.html

Example of verbose logging for fragment cache reads and writes when `enable_fragment_cache_logging` is true.

```text
Read fragment views/v1/2914079/v1/2914079/recordings/70182313-20160225015037000000/d0bdf2974e1ef6d31685c3b392ad0b74 (0.6ms)
Rendered messages/_message.html.erb in 1.2 ms [cache hit]
Write fragment views/v1/2914079/v1/2914079/recordings/70182313-20160225015037000000/3b4e249ac9d168c617e32e84b99218b5 (1.1ms)
Rendered recordings/threads/_thread.html.erb in 1.5 ms [cache miss]
```

--------------------------------

### Fragment Cache Logging Example (Default)

Source: https://guides.rubyonrails.org/v7.0/configuring.html

Example of default logging for fragment cache reads and writes when `enable_fragment_cache_logging` is false.

```text
Rendered messages/_message.html.erb in 1.2 ms [cache hit]
Rendered recordings/threads/_thread.html.erb in 1.5 ms [cache miss]
```

--------------------------------

### Create Article for Partial Layout Example

Source: https://guides.rubyonrails.org/v7.0/action_view_overview.html

This snippet demonstrates creating a new Article record, which is used in the subsequent partial layout example. Ensure the Article model is defined.

```ruby
Article.create(body: 'Partial Layouts are cool!')
```

--------------------------------

### Example Payment Configuration YAML

Source: https://guides.rubyonrails.org/v7.0/configuring.html

A sample `config/payment.yml` file demonstrating environment-specific configurations.

```yaml
production:
  environment: production
  merchant_id: production_merchant_id
  public_key:  production_public_key
  private_key: production_private_key

development:
  environment: sandbox
  merchant_id: development_merchant_id
  public_key:  development_public_key
  private_key: development_private_key
```

--------------------------------

### Generate Kindle Guides

Source: https://guides.rubyonrails.org/v7.0/ruby_on_rails_guides_guidelines.html

Command to generate guides specifically formatted for the Kindle device.

```bash
$ bundle exec rake guides:generate:kindle
```

--------------------------------

### Generate HTML Guides in a Different Language

Source: https://guides.rubyonrails.org/v7.0/ruby_on_rails_guides_guidelines.html

Command to generate guides in a language other than English. Place the language-specific Markdown files in a subdirectory under 'source'.

```bash
$ bundle exec rake guides:generate GUIDES_LANGUAGE=es
```

--------------------------------

### Example CHANGELOG Entry

Source: https://guides.rubyonrails.org/v7.0/contributing_to_ruby_on_rails.html

An example of a CHANGELOG entry, including a summary, code example, and issue reference. Use this format when adding or removing features, fixing bugs, or adding deprecations.

```markdown
*   Summary of a change that briefly describes what was changed. You can use multiple
    lines and wrap them at around 80 characters. Code examples are ok, too, if needed:

        class Foo
          def bar
            puts 'baz'
          end
        end

    You can continue after the code example, and you can attach the issue number.

    Fixes #1234.

    *Your Name*

```

--------------------------------

### Verify Rails Installation

Source: https://guides.rubyonrails.org/v7.0/getting_started.html

After installation, verify that Rails is correctly set up by checking its version. A successful output will display the installed Rails version, such as 'Rails 7.0.0'.

```bash
$ rails --version

```

--------------------------------

### Install Project Dependencies with Bundler

Source: https://guides.rubyonrails.org/v7.0/development_dependencies_install.html

Install all project dependencies using Bundler. This command installs gems required for the project, including those for Active Record tests.

```bash
$ bundle install
```

--------------------------------

### Installing Webpacker

Source: https://guides.rubyonrails.org/v7.0/upgrading_ruby_on_rails.html

Provides the command to install Webpacker after adding it to the Gemfile. This command sets up Webpacker in your Rails application.

```shell
$ bin/rails webpacker:install

```

--------------------------------

### Start Rails Server

Source: https://guides.rubyonrails.org/v7.0/command_line.html

Command to start the Puma server for a Rails application.

```bash
$ bin/rails server
=> Booting Puma...
```

--------------------------------

### Install All Dependencies on Ubuntu

Source: https://guides.rubyonrails.org/v7.0/development_dependencies_install.html

Installs essential development tools and services for Ruby on Rails on Ubuntu using apt-get. This includes databases, caching, image/video processing, and PDF tools.

```bash
$ sudo apt-get update
$ sudo apt-get install sqlite3 libsqlite3-dev mysql-server libmysqlclient-dev postgresql postgresql-client postgresql-contrib libpq-dev redis-server memcached imagemagick ffmpeg mupdf mupdf-tools libxml2-dev

# Install Yarn
$ curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -
$ echo "deb https://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
$ sudo apt-get install yarn

```

--------------------------------

### Install All Dependencies on FreeBSD

Source: https://guides.rubyonrails.org/v7.0/development_dependencies_install.html

Installs necessary development packages for Ruby on Rails on FreeBSD using pkg. Includes database clients/servers, caching, and multimedia tools. Redis can be installed via pkg or ports.

```bash
$ pkg install sqlite3 mysql80-client mysql80-server postgresql11-client postgresql11-server memcached imagemagick ffmpeg mupdf yarn libxml2
# portmaster databases/redis

```

--------------------------------

### Install Webpacker in an Existing Rails Project

Source: https://guides.rubyonrails.org/v7.0/webpacker.html

Add the `webpacker` gem to your `Gemfile`, run `bundle install`, and then execute the Webpacker installation command.

```bash
bundle install
bin/rails webpacker:install
```

--------------------------------

### Install Rails Gem

Source: https://guides.rubyonrails.org/v7.0/getting_started.html

Use RubyGems to install the Rails framework. This command fetches and installs the latest stable version of Rails.

```bash
$ gem install rails

```

--------------------------------

### Start Active Storage (NPM Package)

Source: https://guides.rubyonrails.org/v7.0/active_storage_overview.html

Import and start Active Storage when using it as an npm package in your JavaScript application.

```javascript
import * as ActiveStorage from "@rails/activestorage"
ActiveStorage.start()

```

--------------------------------

### Builder RSS Feed Example

Source: https://guides.rubyonrails.org/v7.0/action_view_overview.html

Provides a full-length example of generating an RSS feed using the Builder library, including channel and item elements.

```ruby
xml.rss("version" => "2.0", "xmlns:dc" => "http://purl.org/dc/elements/1.1/") do
  xml.channel do
    xml.title(@feed_title)
    xml.link(@url)
    xml.description "Basecamp: Recent items"
    xml.language "en-us"
    xml.ttl "40"

    for item in @recent_items
      xml.item do
        xml.title(item_title(item))
        xml.description(item_description(item)) if item_description(item)
        xml.pubDate(item_pubDate(item))
        xml.guid(@person.firm.account.url + @recent_items.url(item))
        xml.link(@person.firm.account.url + @recent_items.url(item))
        xml.tag!("dc:creator", item.author_name) if item_has_creator?(item)
      end
    end
  end
end

```

--------------------------------

### Configure Primary Database

Source: https://guides.rubyonrails.org/v7.0/active_record_multiple_databases.html

Example of a basic single database configuration in `database.yml`.

```yaml
production:
  database: my_primary_database
  adapter: mysql2
  username: root
  password: <%= ENV['ROOT_PASSWORD'] %>

```

--------------------------------

### Example Rails Middleware Stack

Source: https://guides.rubyonrails.org/v7.0/rails_on_rack.html

An example output of the `bin/rails middleware` command, illustrating the default middlewares in a freshly generated Rails application. This shows the order and types of middlewares used.

```text
use Rack::Sendfile
use ActionDispatch::Static
use ActionDispatch::Executor
use ActiveSupport::Cache::Strategy::LocalCache::Middleware
use Rack::Runtime
use Rack::MethodOverride
use ActionDispatch::RequestId
use ActionDispatch::RemoteIp
use Sprockets::Rails::QuietAssets
use Rails::Rack::Logger
use ActionDispatch::ShowExceptions
use WebConsole::Middleware
use ActionDispatch::DebugExceptions
use ActionDispatch::ActionableExceptions
use ActionDispatch::Reloader
use ActionDispatch::Callbacks
use ActiveRecord::Migration::CheckPending
use ActionDispatch::Cookies
use ActionDispatch::Session::CookieStore
use ActionDispatch::Flash
use ActionDispatch::ContentSecurityPolicy::Middleware
use Rack::Head
use Rack::ConditionalGet
use Rack::ETag
use Rack::TempfileReaper
run MyApp::Application.routes
```

--------------------------------

### Install All Dependencies on Fedora or CentOS

Source: https://guides.rubyonrails.org/v7.0/development_dependencies_install.html

Installs necessary development packages for Ruby on Rails on Fedora or CentOS using dnf. Includes database, caching, and multimedia tools. Also covers Yarn installation.

```bash
$ sudo dnf install sqlite-devel sqlite-libs mysql-server mysql-devel postgresql-server postgresql-devel redis memcached imagemagick ffmpeg mupdf libxml2-devel

# Install Yarn
# Use this command if you do not have Node.js installed
$ curl --silent --location https://rpm.nodesource.com/setup_8.x | sudo bash -
# If you have Node.js installed, use this command instead
$ curl --silent --location https://dl.yarnpkg.com/rpm/yarn.repo | sudo tee /etc/apt/sources.list.d/yarn.repo
$ sudo dnf install yarn

```

--------------------------------

### Live Streaming Lyrics Example

Source: https://guides.rubyonrails.org/v7.0/action_controller_overview.html

An example demonstrating how to stream song lyrics line by line in a karaoke fashion using ActionController::Live. This ensures each line is sent only after the previous one has been 'sung'.

```ruby
class LyricsController < ActionController::Base
  include ActionController::Live

  def show
    response.headers['Content-Type'] = 'text/event-stream'
    song = Song.find(params[:id])

    song.each do |line|
      response.stream.write line.lyrics
      sleep line.num_beats
    end
  ensure
    response.stream.close
  end
end
```

--------------------------------

### CSS Manifest File Example

Source: https://guides.rubyonrails.org/v7.0/asset_pipeline.html

Example of a CSS manifest file using Sprockets directives to include self and all CSS files in the current directory.

```css
/* ...
 *= require_self
 *= require_tree .
 */

```

--------------------------------

### Simulate GET Request with Headers

Source: https://guides.rubyonrails.org/v7.0/testing.html

Demonstrates how to simulate a GET request to a specific resource, including passing custom HTTP headers. Useful for testing authentication or referer checks.

```ruby
get article_url(Article.first), headers: { "HTTP_REFERER" => "http://example.com/home" }
```

--------------------------------

### Setup the Database

Source: https://guides.rubyonrails.org/v7.0/active_record_migrations.html

Creates the database, loads the schema, and initializes it with seed data. This command is used for setting up a new development environment.

```bash
$ bin/rails db:setup
```

--------------------------------

### GET Request to Patients URL

Source: https://guides.rubyonrails.org/v7.0/routing.html

Example of an incoming GET request for a specific patient URL.

```text
GET /patients/17
```

--------------------------------

### JavaScript Manifest File Example

Source: https://guides.rubyonrails.org/v7.0/asset_pipeline.html

Example of a JavaScript manifest file using Sprockets directives to include necessary libraries and all JavaScript files in the current directory.

```javascript
// ...
//= require rails-ujs
//= require turbolinks
//= require_tree .

```

--------------------------------

### Start Rails Server

Source: https://guides.rubyonrails.org/v7.0/getting_started.html

Run this command in your Rails application's root directory to start the development server. For Windows users, use 'ruby bin\rails server'.

```bash
$ bin/rails server

```

--------------------------------

### Rack::Server#start Method

Source: https://guides.rubyonrails.org/v7.0/initialization.html

Initiates the Rack server startup process, handling options like warnings, load paths, debugging, and daemonization.

```Ruby
module Rack
  class Server
    def start &blk
      if options[:warn]
        $-w = true
      end

      if includes = options[:include]
        $LOAD_PATH.unshift(*includes)
      end

      if library = options[:require]
        require library
      end

      if options[:debug]
        $DEBUG = true
        require "pp"
        p options[:server]
        pp wrapped_app
        pp app
      end

      check_pid! if options[:pid]

      # Touch the wrapped app, so that the config.ru is loaded before
      # daemonization (i.e. before chdir, etc).
      handle_profiling(options[:heapfile], options[:profile_mode], options[:profile_file]) do
        wrapped_app
      end

      daemonize_app if options[:daemonize]

      write_pid if options[:pid]

      trap(:INT) do
        if server.respond_to?(:shutdown)
          server.shutdown
        else
          exit
        end
      end

      server.run wrapped_app, options, &blk
    end
  end
end

```

--------------------------------

### Require config/application.rb

Source: https://guides.rubyonrails.org/v7.0/initialization.html

The `config/environment.rb` file starts by requiring `config/application.rb`. This is a fundamental step in setting up the Rails environment.

```ruby
require_relative "application"

```

--------------------------------

### RDoc Example: Attribute Reader

Source: https://guides.rubyonrails.org/v7.0/api_documentation_guidelines.html

Example of an RDoc comment for an attribute reader method. Comments should start with an uppercase letter and follow standard punctuation rules.

```ruby
# Declares an attribute reader backed by an internally-named
# instance variable.
def attr_internal_reader(*attrs)
  # ...
end

```

--------------------------------

### Refactored Controller Tests with Setup and Teardown

Source: https://guides.rubyonrails.org/v7.0/testing.html

Demonstrates refactoring controller tests using `setup` and `teardown` callbacks to reduce duplication and manage instance variables and cache clearing.

```ruby
require "test_helper"

class ArticlesControllerTest < ActionDispatch::IntegrationTest
  # called before every single test
  setup do
    @article = articles(:one)
  end

  # called after every single test
  teardown do
    # when controller is using cache it may be a good idea to reset it afterwards
    Rails.cache.clear
  end

  test "should show article" do
    # Reuse the @article instance variable from setup
    get article_url(@article)
    assert_response :success
  end

  test "should destroy article" do
    assert_difference("Article.count", -1) do
      delete article_url(@article)
    end

    assert_redirected_to articles_path
  end

  test "should update article" do
    patch article_url(@article), params: { article: { title: "updated" } }

    assert_redirected_to article_path(@article)
    # Reload association to fetch updated data and assert that title is updated.
    @article.reload
    assert_equal "updated", @article.title
  end
end

```

--------------------------------

### Example: Generate Greetings Controller with Hello Action

Source: https://guides.rubyonrails.org/v7.0/command_line.html

Generates a `Greetings` controller with a `hello` action. This command also sets up the route for the action and creates the necessary view and test files.

```bash
$ bin/rails generate controller Greetings hello
```

--------------------------------

### Application Template for Devise Installation

Source: https://guides.rubyonrails.org/v7.0/generators.html

An application template script that conditionally installs Devise, prompts for the user model name, and runs necessary setup commands.

```ruby
# template.rb

if yes?("Would you like to install Devise?")
  gem "devise"
  devise_model = ask("What would you like the user model to be called?", default: "User")
end

after_bundle do
  if devise_model
    generate "devise:install"
    generate "devise", devise_model
    rails_command "db:migrate"
  end

  git add: ".", commit: %(-m 'Initial commit')
end


```

--------------------------------

### config/boot.rb for Bundler setup

Source: https://guides.rubyonrails.org/v7.0/initialization.html

Initializes Bundler by setting the `BUNDLE_GEMFILE` environment variable and requiring `bundler/setup` to configure the gem load path.

```ruby
ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../Gemfile', __dir__)

require "bundler/setup" # Set up gems listed in the Gemfile.

```

--------------------------------

### Get Substring from Position

Source: https://guides.rubyonrails.org/v7.0/active_support_core_extensions.html

Returns the substring starting from a given position. Supports positive, negative, and out-of-bounds indices, returning nil if the start position is beyond the string length.

```ruby
"hello".from(0)  # => "hello"
"hello".from(2)  # => "llo"
"hello".from(-2) # => "lo"
"hello".from(10) # => nil
```

--------------------------------

### Simple YAML Translation Example

Source: https://guides.rubyonrails.org/v7.0/i18n.html

A basic example of a translation string in YAML format. This defines a 'hello' key that maps to the 'Hello world' string in the :en locale.

```yaml
en:
  hello: "Hello world"
```

--------------------------------

### Relative File Path Example

Source: https://guides.rubyonrails.org/v7.0/api_documentation_guidelines.html

Demonstrates the correct way to specify file paths relative to the application root.

```Text
config/routes.rb            # YES
routes.rb                   # NO
RAILS_ROOT/config/routes.rb # NO

```

--------------------------------

### Get Beginning and End of Week

Source: https://guides.rubyonrails.org/v7.0/active_support_core_extensions.html

Returns the dates for the beginning and end of the week. Weeks default to starting on Monday, but this can be customized.

```ruby
d = Date.new(2010, 5, 8)     # => Sat, 08 May 2010
d.beginning_of_week          # => Mon, 03 May 2010
d.beginning_of_week(:sunday) # => Sun, 02 May 2010
d.end_of_week                # => Sun, 09 May 2010
d.end_of_week(:sunday)       # => Sat, 08 May 2010
```

--------------------------------

### Key Rotation Configuration Example

Source: https://guides.rubyonrails.org/v7.0/active_record_encryption.html

Example configuration for key rotation using a list of primary keys. The last key is used for encrypting new content, while all keys are tried for decryption.

```yaml
active_record_encryption:
  primary_key:
    - a1cc4d7b9f420e40a337b9e68c5ecec6 # Previous keys can still decrypt existing content
    - bc17e7b413fd4720716a7633027f8cc4 # Active, encrypts new content
  key_derivation_salt: a3226b97b3b2f8372d1fc6d497a0c0d3
```

--------------------------------

### Install Webpacker in a New Rails Project

Source: https://guides.rubyonrails.org/v7.0/webpacker.html

Add the `--webpack` flag to the `rails new` command to include Webpacker from the start.

```bash
rails new myapp --webpack
```

--------------------------------

### Reset the Database

Source: https://guides.rubyonrails.org/v7.0/active_record_migrations.html

Drops the existing database and then sets it up again from scratch. This is equivalent to running `db:drop` followed by `db:setup`.

```bash
$ bin/rails db:reset
```

--------------------------------

### Markdown Headings Structure

Source: https://guides.rubyonrails.org/v7.0/ruby_on_rails_guides_guidelines.html

Demonstrates the expected heading structure in Markdown for guide titles, sections, and subsections. The generated HTML will start with h2 tags.

```markdown
Guide Title
===========

Section
-------

### Sub Section
```

--------------------------------

### Rackup Command Help

Source: https://guides.rubyonrails.org/v7.0/rails_on_rack.html

Displays help information for the `rackup` command, useful for understanding its various options.

```bash
$ rackup --help
```

--------------------------------

### Creating a Specific Database

Source: https://guides.rubyonrails.org/v7.0/active_record_multiple_databases.html

Demonstrates how to create a specific database, such as the 'animals' database, using a dedicated Rails command.

```bash
bin/rails db:create:animals
```

--------------------------------

### Getting All Parent Modules with `module_parents`

Source: https://guides.rubyonrails.org/v7.0/active_support_core_extensions.html

The `module_parents` method returns an array of all containing modules, starting from the immediate parent up to `Object`. This is useful for traversing the module hierarchy.

```Ruby
module X
  module Y
    module Z
    end
  end
end
M = X::Y::Z

X::Y::Z.module_parents # => [X::Y, X, Object]
M.module_parents       # => [X::Y, X, Object]
```

--------------------------------

### Install JavaScript Dependencies

Source: https://guides.rubyonrails.org/v7.0/development_dependencies_install.html

Install JavaScript dependencies using Yarn. Ensure Yarn is installed prior to running this command.

```bash
$ yarn install
```

--------------------------------

### Create Database with bin/rails db:create

Source: https://guides.rubyonrails.org/v7.0/command_line.html

Creates the application's database.

```bash
bin/rails db:create
```

--------------------------------

### Controller with Responders

Source: https://guides.rubyonrails.org/v7.0/upgrading_ruby_on_rails.html

Example of a controller using respond_to and respond_with after adding the responders gem.

```ruby
class UsersController < ApplicationController
  respond_to :html, :json

  def show
    @user = User.find(params[:id])
    respond_with @user
  end
end
```

--------------------------------

### Home View Index Template

Source: https://guides.rubyonrails.org/v7.0/i18n.html

Renders a "Hello World" heading and displays the flash notice.

```erb
<h1>Hello World</h1>
<p><%= flash[:notice] %></p>
```

--------------------------------

### Verify SQLite3 Installation

Source: https://guides.rubyonrails.org/v7.0/getting_started.html

Confirm that SQLite3 is installed and accessible in your system's load path. The command should output the installed version number.

```bash
$ sqlite3 --version

```

--------------------------------

### Specify Start ID for find_in_batches

Source: https://guides.rubyonrails.org/v7.0/active_record_querying.html

Retrieves records starting from a specific ID using the `start` option. Useful for resuming interrupted batch processes.

```ruby
Customer.find_in_batches(batch_size: 2500, start: 5000) do |customers|
  export.add_customers(customers)
end
```

--------------------------------

### MySQL/MariaDB EXPLAIN output for eager loading

Source: https://guides.rubyonrails.org/v7.0/active_record_querying.html

Example `EXPLAIN` output for a query involving eager loading on MySQL/MariaDB, showing separate plans for the main query and the included associations.

```text
EXPLAIN for: SELECT `customers`.* FROM `customers`  WHERE `customers`.`id` = 1
+----+-------------+-----------+-------+---------------+---------+---------+-------+------+------+
| id | select_type | table     | type  | possible_keys | key     | key_len | ref   | rows | Extra|
+----+-------------+-----------+-------+---------------+---------+---------+-------+------+------+
|  1 | SIMPLE      | customers | const | PRIMARY       | PRIMARY | 4       | const |    1 |      |
+----+-------------+-----------+-------+---------------+---------+---------+-------+------+------+

1 row in set (0.00 sec)

EXPLAIN for: SELECT `orders`.* FROM `orders`  WHERE `orders`.`customer_id` IN (1)
+----+-------------+--------+------+---------------+------+---------+------+------+-------------+
| id | select_type | table  | type | possible_keys | key  | key_len | ref  | rows | Extra       |
+----+-------------+--------+------+---------------+------+---------+------+------+-------------+
|  1 | SIMPLE      | orders | ALL  | NULL          | NULL | NULL    | NULL |    1 | Using where |
+----+-------------+--------+------+---------------+------+---------+------+------+-------------+


1 row in set (0.00 sec)
```

--------------------------------

### Define Models for Form Examples

Source: https://guides.rubyonrails.org/v7.0/form_helpers.html

Defines simple ApplicationRecord models for demonstrating form helpers.

```ruby
class City < ApplicationRecord
end

class Person < ApplicationRecord
  belongs_to :city
end
```

--------------------------------

### PostgreSQL EXPLAIN output for eager loading

Source: https://guides.rubyonrails.org/v7.0/active_record_querying.html

Example `EXPLAIN` output for a query involving eager loading on PostgreSQL, showing the SQL statements executed and their respective query plans.

```text
  Customer Load (0.3ms)  SELECT "customers".* FROM "customers" WHERE "customers"."id" = $1  [["id", 1]]
  Order Load (0.3ms)  SELECT "orders".* FROM "orders" WHERE "orders"."customer_id" = $1  [["customer_id", 1]]
=> EXPLAIN for: SELECT "customers".* FROM "customers" WHERE "customers"."id" = $1 [["id", 1]]
                                    QUERY PLAN
----------------------------------------------------------------------------------
 Index Scan using customers_pkey on customers  (cost=0.15..8.17 rows=1 width=164)
   Index Cond: (id = '1'::bigint)
(2 rows)
```

--------------------------------

### Install RubyGems Dependencies

Source: https://guides.rubyonrails.org/v7.0/contributing_to_ruby_on_rails.html

Installs all the required RubyGems for the Rails project.

```bash
$ bundle install

```

--------------------------------

### Example: Generate CreditCards Controller

Source: https://guides.rubyonrails.org/v7.0/command_line.html

Generates a `CreditCards` controller with `open`, `debit`, `credit`, `close` actions. This includes creating associated view files and tests.

```bash
$ bin/rails generate controller CreditCards open debit credit close
```

--------------------------------

### Run Tests with Full Backtrace

Source: https://guides.rubyonrails.org/v7.0/testing.html

Demonstrates how to run tests and include the full backtrace in the output by using the `-b` or `--backtrace` command-line argument. This is useful for debugging framework-level issues.

```shell
$ bin/rails test -b test/models/article_test.rb

```

--------------------------------

### Install Bundler Gem

Source: https://guides.rubyonrails.org/v7.0/development_dependencies_install.html

Install or update the Bundler gem to manage project dependencies.

```bash
$ gem install bundler
$ gem update bundler
```

--------------------------------

### Rails Server Initialization

Source: https://guides.rubyonrails.org/v7.0/rails_on_rack.html

Shows how `bin/rails server` creates a `Rack::Server` object and starts the web server. This code is part of the `Rails::Server` class, which inherits from `Rack::Server`.

```ruby
Rails::Server.new.tap do |server|
  require APP_PATH
  Dir.chdir(Rails.application.root)
  server.start
end
```

```ruby
class Server < ::Rack::Server
  def start
    # ...
    super
  end
end
```

--------------------------------

### Fingerprinted CSS Filename Example

Source: https://guides.rubyonrails.org/v7.0/asset_pipeline.html

An example of a CSS filename after fingerprinting, where a hash of the content is appended.

```text
global-908e25f4bf641868d8683022a5b62f54.css
```

--------------------------------

### Configure PostgreSQL User for Testing (Linux/BSD)

Source: https://guides.rubyonrails.org/v7.0/development_dependencies_install.html

Set up a superuser for PostgreSQL on Linux or BSD systems using the current user.

```bash
$ sudo -u postgres createuser --superuser $USER
```

--------------------------------

### Navigate to Application Directory

Source: https://guides.rubyonrails.org/v7.0/getting_started.html

After creating the application, change your current directory to the newly created application folder using the `cd` command.

```bash
cd blog

```

--------------------------------

### View Plugin Generator Options

Source: https://guides.rubyonrails.org/v7.0/engines.html

Run this command to see all available options for the plugin generator.

```bash
$ rails plugin --help

```

--------------------------------

### Configure Multiple Databases

Source: https://guides.rubyonrails.org/v7.0/active_record_multiple_databases.html

Example of a `database.yml` configuration for multiple databases, including primary, replicas, and a separate database for 'animals' with its own replica.

```yaml
production:
  primary:
    database: my_primary_database
    username: root
    password: <%= ENV['ROOT_PASSWORD'] %>
    adapter: mysql2
  primary_replica:
    database: my_primary_database
    username: root_readonly
    password: <%= ENV['ROOT_READONLY_PASSWORD'] %>
    adapter: mysql2
    replica: true
  animals:
    database: my_animals_database
    username: animals_root
    password: <%= ENV['ANIMALS_ROOT_PASSWORD'] %>
    adapter: mysql2
    migrations_paths: db/animals_migrate
  animals_replica:
    database: my_animals_database
    username: animals_readonly
    password: <%= ENV['ANIMALS_READONLY_PASSWORD'] %>
    adapter: mysql2
    replica: true

```

--------------------------------

### Print all defined initializers

Source: https://guides.rubyonrails.org/v7.0/command_line.html

Lists all initializers in the order they are invoked by Rails.

```bash
bin/rails initializers

```

--------------------------------

### Engine Initialization File

Source: https://guides.rubyonrails.org/v7.0/engines.html

The `lib/blorgh.rb` file requires the engine's engine file and defines the base module. It can also be used for global configuration.

```ruby
require "blorgh/engine"

module Blorgh
end

```

--------------------------------

### S3 CORS Configuration Example

Source: https://guides.rubyonrails.org/v7.0/active_storage_overview.html

Example CORS configuration for Amazon S3 to allow direct upload requests from your application.

```json
[
  {
    "AllowedHeaders": [
      "*"
    ],
    "AllowedMethods": [
      "PUT"
    ],
    "AllowedOrigins": [
      "https://www.example.com"
    ],
    "ExposeHeaders": [
      "Origin",
      "Content-Type",
      "Content-MD5",
      "Content-Disposition"
    ],
    "MaxAgeSeconds": 3600
  }
]

```

--------------------------------

### Direct Rendering with Instance Variables and Flash

Source: https://guides.rubyonrails.org/v7.0/layouts_and_rendering.html

Demonstrates how to directly render a template (e.g., 'index') and populate instance variables and flash messages when a record is not found, avoiding an extra browser round trip.

```ruby
def index
  @books = Book.all
end

def show
  @book = Book.find_by(id: params[:id])
  if @book.nil?
    @books = Book.all
    flash.now[:alert] = "Your book was not found"
    render "index"
  end
end
```

--------------------------------

### Example Log Entry of Cookie Theft

Source: https://guides.rubyonrails.org/v7.0/security.html

This is an example of what an attacker's web server access log might look like after a successful cookie theft attempt using the previous XSS example. It shows the stolen cookie appended to the requested URL.

```text
GET http://www.attacker.com/_app_session=836c1c25278e5b321d6bea4f19cb57e2

```

--------------------------------

### Wrapped JSON Parameters Example

Source: https://guides.rubyonrails.org/v7.0/action_controller_overview.html

This example shows how JSON parameters are wrapped with a key based on the controller name when `wrap_parameters` is active.

```json
{ name: "acme", address: "123 Carrot Street", company: { name: "acme", address: "123 Carrot Street" } }

```

--------------------------------

### Google Cloud Storage CORS Configuration Example

Source: https://guides.rubyonrails.org/v7.0/active_storage_overview.html

Example CORS configuration for Google Cloud Storage to permit direct upload requests.

```json
[
  {
    "origin": ["https://www.example.com"],
    "method": ["PUT"],
    "responseHeader": ["Origin", "Content-Type", "Content-MD5", "Content-Disposition"],
    "maxAgeSeconds": 3600
  }
]

```

--------------------------------

### Rack::Handler::Puma Run Method

Source: https://guides.rubyonrails.org/v7.0/initialization.html

Illustrates the `run` method for the Puma server handler, showing how it configures and launches the Puma server with the provided application and options.

```ruby
module Rack
  module Handler
    module Puma
      # ...
      def self.run(app, options = {})
        conf   = self.config(app, options)

        events = options.delete(:Silent) ? ::Puma::Events.strings : ::Puma::Events.stdio

        launcher = ::Puma::Launcher.new(conf, :events => events)

        yield launcher if block_given?
        begin
          launcher.run
        rescue Interrupt
          puts "* Gracefully stopping, waiting for requests to finish"
          launcher.stop
          puts "* Goodbye!"
        end
      end
      # ...
    end
  end
end

```

--------------------------------

### Install Engine Migrations

Source: https://guides.rubyonrails.org/v7.0/engines.html

Command to copy migration files from the 'blorgh' engine into the application's `db/migrate` directory. This ensures the engine's database schema is created in the application.

```bash
$ bin/rails blorgh:install:migrations

```

--------------------------------

### Old Rails Query String Cache Busting Example

Source: https://guides.rubyonrails.org/v7.0/asset_pipeline.html

An example of how older Rails versions appended a date-based query string for cache busting.

```text
/stylesheets/global.css?1309495796
```

--------------------------------

### Configuring Reloadable Code with `to_prepare`

Source: https://guides.rubyonrails.org/v7.0/autoloading_and_reloading_constants.html

Shows how to correctly configure reloadable constants within initializers by wrapping the code in a `to_prepare` block, ensuring it runs on boot and after each reload.

```ruby
# config/initializers/api_gateway_setup.rb
Rails.application.config.to_prepare do
  ApiGateway.endpoint = "https://example.com" # CORRECT
end

```

--------------------------------

### Azure Storage CORS Configuration Example

Source: https://guides.rubyonrails.org/v7.0/active_storage_overview.html

Example CORS configuration for Azure Storage, specifying allowed origins, methods, and headers for direct uploads.

```xml
<Cors>
  <CorsRule>
    <AllowedOrigins>https://www.example.com</AllowedOrigins>
    <AllowedMethods>PUT</AllowedMethods>
    <AllowedHeaders>Origin, Content-Type, Content-MD5, x-ms-blob-content-disposition, x-ms-blob-type</AllowedHeaders>
    <MaxAgeInSeconds>3600</MaxAgeInSeconds>
  </CorsRule>
</Cors>

```

--------------------------------

### Cache Key Example

Source: https://guides.rubyonrails.org/v7.0/caching_with_rails.html

An example of a cache key generated by Rails for a view fragment. The template tree digest changes if the view fragment is modified.

```text
views/products/index:bea67108094918eeba42cd4a6e786901/products/1

```

--------------------------------

### Interactive Example for after_save_commit

Source: https://guides.rubyonrails.org/v7.0/active_record_callbacks.html

This interactive example demonstrates the behavior of the `after_save_commit` alias when creating and updating a User record, showing the output of the associated callback.

```irb
irb> @user = User.create # creating a User
User was saved to database

irb> @user.save # updating @user
User was saved to database
```

--------------------------------

### Parallel Testing with Setup and Teardown Hooks

Source: https://guides.rubyonrails.org/v7.0/testing.html

Use `parallelize_setup` and `parallelize_teardown` hooks for tasks that need to run after forking and before closing processes, such as managing multiple databases.

```ruby
class ActiveSupport::TestCase
  parallelize_setup do |worker|
    # setup databases
  end

  parallelize_teardown do |worker|
    # cleanup databases
  end

  parallelize(workers: :number_of_processors)
end

```

--------------------------------

### Add Collection Route with GET Verb

Source: https://guides.rubyonrails.org/v7.0/routing.html

Defines a 'search' collection route for 'photos' using a `collection` block, recognizing GET requests to `/photos/search`.

```ruby
resources :photos do
  collection do
    get 'search'
  end
end
```

--------------------------------

### after_initialize and after_find Callback Execution

Source: https://guides.rubyonrails.org/v7.0/active_record_callbacks.html

Shows the output when creating a new user and finding an existing user, illustrating when `after_initialize` and `after_find` are triggered.

```irb
irb> User.new
You have initialized an object!
=> #<User id: nil>

irb> User.first
You have found an object!
You have initialized an object!
=> #<User id: 1>
```

--------------------------------

### Validate Generated HTML Guides

Source: https://guides.rubyonrails.org/v7.0/ruby_on_rails_guides_guidelines.html

Command to validate the generated HTML guides. This helps catch issues like duplicate IDs generated from heading titles.

```bash
$ bundle exec rake guides:validate
```

--------------------------------

### Start Rails Development Server

Source: https://guides.rubyonrails.org/v7.0/command_line.html

Starts the Rails development server, typically used for local development and testing. Access your application via http://localhost:3000.

```bash
$ bin/rails server
```

--------------------------------

### Generate Scaffold with Custom Generator

Source: https://guides.rubyonrails.org/v7.0/generators.html

Demonstrates running the scaffold generator after configuring custom generators and fallbacks, showing the custom generator being invoked.

```bash
$ bin/rails generate scaffold Comment body:text
      invoke  active_record
      create    db/migrate/20230518000000_create_comments.rb
      create    app/models/comment.rb
      invoke    my_test_unit
    Doing different stuff...
      invoke  resource_route
       route    resources :comments
      invoke  scaffold_controller
      create    app/controllers/comments_controller.rb
      invoke    erb
      create      app/views/comments
      create      app/views/comments/index.html.erb
      create      app/views/comments/edit.html.erb
      create      app/views/comments/show.html.erb
      create      app/views/comments/new.html.erb
      create      app/views/comments/_form.html.erb
      create      app/views/comments/_comment.html.erb
      invoke    resource_route
      invoke    my_test_unit
      create      test/controllers/comments_controller_test.rb
      create      test/system/comments_test.rb
      invoke    helper
      create      app/helpers/comments_helper.rb
      invoke      my_test_unit
    invoke    jbuilder
      create      app/views/comments/index.json.jbuilder
      create      app/views/comments/show.json.jbuilder


```

--------------------------------

### Get Integer Ordinal Suffix

Source: https://guides.rubyonrails.org/v7.0/active_support_core_extensions.html

Use `ordinal` to get the ordinal suffix (st, nd, rd, th) for an integer. Handles positive and negative numbers.

```ruby
1.ordinal    # => "st"
2.ordinal    # => "nd"
53.ordinal   # => "rd"
2009.ordinal # => "th"
-21.ordinal  # => "st"
-134.ordinal # => "th"
```

--------------------------------

### SQL for includes (2 queries)

Source: https://guides.rubyonrails.org/v7.0/active_record_querying.html

These SQL queries illustrate the efficient loading achieved by `includes`. The first query fetches the books, and the second fetches all associated authors in a single query.

```sql
SELECT books.* FROM books LIMIT 10
SELECT authors.* FROM authors
  WHERE authors.book_id IN (1,2,3,4,5,6,7,8,9,10)

```

--------------------------------

### Run EXPLAIN on a basic query

Source: https://guides.rubyonrails.org/v7.0/active_record_querying.html

Use `explain` to see the query plan for a simple Active Record query. The output format varies depending on the database adapter.

```ruby
Customer.where(id: 1).joins(:orders).explain
```

--------------------------------

### Add Member Route with GET Verb

Source: https://guides.rubyonrails.org/v7.0/routing.html

Defines a 'preview' member route for 'photos' using a `member` block, which recognizes GET requests to `/photos/:id/preview`.

```ruby
resources :photos do
  member do
    get 'preview'
  end
end
```

--------------------------------

### Install All Railties Migrations

Source: https://guides.rubyonrails.org/v7.0/engines.html

Command to copy migration files from all installed railties (including engines) into the application's `db/migrate` directory. Use this if you have multiple engines with migrations.

```bash
$ bin/rails railties:install:migrations

```

--------------------------------

### Configure PostgreSQL User for Testing (macOS)

Source: https://guides.rubyonrails.org/v7.0/development_dependencies_install.html

Set up a superuser for PostgreSQL on macOS using the current user.

```bash
$ createuser --superuser $USER
```

--------------------------------

### Run EXPLAIN with eager loading

Source: https://guides.rubyonrails.org/v7.0/active_record_querying.html

Use `explain` with `includes` to analyze the query plans generated for eager loading. This may result in multiple queries being explained.

```ruby
Customer.where(id: 1).includes(:orders).explain
```

--------------------------------

### Specify Start and Finish IDs with find_each

Source: https://guides.rubyonrails.org/v7.0/active_record_querying.html

Use `:start` and `:finish` options together with `find_each` to process a specific range of records based on their primary key IDs.

```ruby
Customer.find_each(start: 2000, finish: 10000) do |customer|
  NewsMailer.weekly(customer).deliver_now
end
```

--------------------------------

### Specify Start ID with find_each

Source: https://guides.rubyonrails.org/v7.0/active_record_querying.html

Use the `:start` option with `find_each` to begin processing records from a specific primary key ID, useful for resuming interrupted processes.

```ruby
Customer.find_each(start: 2000) do |customer|
  NewsMailer.weekly(customer).deliver_now
end
```

--------------------------------

### CSRF Protection for JavaScript GET Requests

Source: https://guides.rubyonrails.org/v7.0/upgrading_ruby_on_rails.html

Switch from `get` to `xhr` when testing JavaScript responses to explicitly test an XmlHttpRequest and avoid triggering CSRF protection unexpectedly.

```ruby
get :index, format: :js
```

```ruby
xhr :get, :index, format: :js
```

--------------------------------

### Sample YAML Fixture File

Source: https://guides.rubyonrails.org/v7.0/testing.html

This is an example of a human-friendly YAML fixture file for defining sample data. Each record is separated by a blank line, and comments can be added using the '#' character.

```yaml
# lo & behold! I am a YAML comment!
david:
  name: David Heinemeier Hansson
  birthday: 1979-10-15
  profession: Systems development

steve:
  name: Steve Ross Kellock
  birthday: 1974-09-27
  profession: guy with keyboard

```

--------------------------------

### Get Integer Ordinal String

Source: https://guides.rubyonrails.org/v7.0/active_support_core_extensions.html

Use `ordinalize` to get the full ordinal string representation of an integer, including the number and its suffix. Handles positive and negative numbers.

```ruby
1.ordinalize    # => "1st"
2.ordinalize    # => "2nd"
53.ordinalize   # => "53rd"
2009.ordinalize # => "2009th"
-21.ordinalize  # => "-21st"
-134.ordinalize # => "-134th"
```

--------------------------------

### Add Gem Dependency

Source: https://guides.rubyonrails.org/v7.0/engines.html

Specify a gem dependency that should be installed with the engine during a traditional `gem install`. This is done within the `Gem::Specification` block in the engine's .gemspec file.

```ruby
s.add_dependency "moo"
```