By NinjaPoulp in Cheatsheets — 05 May 2025

Ruby on Rails

Basics

Rails is a cool and expressive ruby framework aimed at web developement.
It is pragmatic in its philosophy, and thus uses an opinionated convention over configuration approach to developement.
Code looks nice and non bloated.
While not the most popular out there, ruby language has a strong community of developpers, making ruby packages available as "gems".

Requirements

Rails is a so-called ruby gem and needs to be installed with

$ gem install rails

A useful gem to install alongside is called bundler and allows dependencies bundling

$ gem install bundler

Kickstarting a rails app is as easy as running

$ rails new appname

This command creates a new folder called appname containing the application files
Using the bundler gem one can update and install gems specified in the file called Gemfile

$ bundle update && bundle install

Launching a server is achieved with

$ rails server -p $PORT -b $IP

Shortcuts

Rails conventions allows neat shortcuts

initialize database

rake is a gem equivalent to make but ruby flavored

$ rake db:create

launching a rails server

$ rails s

generating a new controller (Pascal case and plural)

$ rails g controller Pictures

One can add options to generate controller methods and associated routes and views
The following create the Pictures controller as well as index and show methods and associated routes

$ rails g controller Pictures index show

generating a model (Pascal singular)

$ rails g model Picture

One cand add options to generate a migration with table columns
The following creates a Picture model with a migration containing two fields: path of type string, and title of type text

$ rails g model Picture path:string title:text

Migrations are used to update db schema, pending migrations can be run with

$ rake db:migrate

To rollback the last migration (CAREFUL destructive operation ahead)

$ rake db:rollback

More in depth

Architecture

Create a new application

Install the Rails gem if you haven't done so before

$ gem install rails

Generate a new Rails app w/ Postgres support

$ rails new my_app --database=postgresql

Initialize the database

$ rake db:create

Start the Rails server

$ rails s

Routes

Create a route that maps a URL to the controller action

# config/routes.rb
get 'welcome' => 'pages#home'

Shorthand for connecting a route to a controller/action

# config/routes.rb
get 'photos/show'

# The above is the same as: 
get 'photos/show', :to 'photos#show'
get 'photos/show' => 'photos#show'

Automagically create all the routes for a RESTful resource

# config/routes.rb
resources :photos

HTTP Verb	Path	Controller#Action	Used for
GET	/photos	photos#index	display a list of all photos
GET	/photos_new	photos#new	return an HTML form for creating a new photo
POST	/photos	photos#create	create a new photo
GET	/photos/:id	photos#show	display a specific photo
GET	/photos/:id/edit	photos#edit	return an HTML form for editing a photo
PATCH/PUT	/photos/:id	photos#update	update a specific photo
DELETE	/photos/:id	photos#destroy	delete a specific photo

Create resources for only certain actions

# config/routes.rb
resources :photos, :only => [:index]

# On the flip side, you can create a resource with exceptions 
resources :photos, :except => [:new, :create, :edit, :update, :show, :destroy]

Create a route to a static view, without an action in the controller

# config/routes.rb
# If there's a file called 'about.html.erb' in 'app/views/photos', this file will be 
#   automatically rendered when you call localhost:3000/photos/about
get 'photos/about', to: 'photos#about'

Reference: http://guides.rubyonrails.org/routing.html

Controllers

Generate a new controller

Note: Name controllers in Pascal case and pluralize

$ rails g controller Photos

Generate a new controller with default actions, routes and views

$ rails g controller Photos index show

Reference: http://guides.rubyonrails.org/action_controller_overview.html

Models

Generate a model and create a migration for the table

Note: Name models in Pascal case and singular

$ rails g model Photo

Generate a model and create a migration with table columns

$ rails g model Photo path:string caption:text

The migration automatically created for the above command:

class CreatePhotos < ActiveRecord::Migration
  def change
    create_table :photos do |t|
      t.string :path
      t.text :caption
 
      t.timestamps null: false
    end
  end
end

Reference: http://guides.rubyonrails.org/active_model_basics.html

Migrations

Migration Data Types

:boolean
:date
:datetime
:decimal
:float
:integer
:primary_key
:references
:string
:text
:time
:timestamp

When the name of the migration follows the format AddXXXToYYY followed by a list of columns, it will add those columns to the existing table

$ rails g migration AddDateTakenToPhotos date_taken:datetime

The above creates the following migration:

class AddDateTakenToPhotos < ActiveRecord::Migration[5.0]
  def change
    add_column :photos, :date_taken, :datetime
  end
end

You can also add a new column to a table with an index

$ rails g migration AddDateTakenToPhotos date_taken:datetime:index

The above command generates the following migration:

class AddDateTakenToPhotos < ActiveRecord::Migration[5.0]
  def change
    add_column :photos, :date_taken, :datetime
    add_index :photos, :date_taken
  end
end

The opposite goes for migration names following the format: RemoveXXXFromYYY

$ rails g migration RemoveDateTakenFromPhotos date_taken:datetime

The above generates the following migration:

class RemoveDateTakenFromPhotos < ActiveRecord::Migration[5.0]
  def change
    remove_column :photos, :date_taken, :datetime
  end
end

Scaffolding

Scaffolding is great for prototypes but don't rely too heavily on it: http://stackoverflow.com/a/25140503

$ rails g scaffold Photo path:string caption:text
$ rake db:migrate

Rake

View all the routes in an application

$ rake routes

Seed the database with sample data from db/seeds.rb

$ rake db:seed

Run any pending migrations

$ rake db:migrate

Rollback the last migration performed

NOTE: Be VERY careful with this command in production, it's destructive and you could potentially lose data. Make sure you absolutely understand what will happen when you run it

$ rake db:rollback

Path Helpers

Creating a path helper for a route

# Creating a path helper for a route
get '/photos/:id', to: 'photos#show', as: 'photo'

# app/controllers/photos_controller.rb
@photo = Photo.find(17)

# View for the action
<%= link_to 'Photo Record', photo_path(@photo) %>

Path helpers are automatically created when specifying a resource in config/routes.rb

# config/routes.rb
resources :photos

HTTP Verb	Path	Controller#Action	Named Helper
GET	/photos	photos#index	photos_path
GET	/photos/new	photos#new	new_photo_path
POST	/photos	photos#create	photos_path
GET	/photos/:id	photos#show	photo_path(:id)
GET	/photos/:id/edit	photos#edit	edit_photo_path(:id)
PATCH/PUT	/photos/:id	photos#update	photo_path(:id)
DELETE	/photos/:id	photos#destroy	photo_path(:id)

Asset Pipeline

Access images in the app/assets/images directory like this:

<%= image_tag "rails.png" %>

Within views, link to JavaScript and CSS assets

<%= stylesheet_link_tag "application" %> 
<%= javascript_include_tag "application" %>

<!-- Filenames are fingerprinted for cache busting -->
<link href="/assets/application-4dd5b109ee3439da54f5bdfd78a80473.css" media="screen"
rel="stylesheet" />
<script src="/assets/application-908e25f4bf641868d8683022a5b62f54.js"></script>

Reference: http://guides.rubyonrails.org/asset_pipeline.html

Form Helpers

Bind a form to a model for creating/updating a resource

Use this method if you're using strong params to protect against mass assignment

# app/controllers/photos_controller.rb
def new
  @photo = Photo.new
end

# ERB view
<%= form_for @photo, url: {action: "create"}, html: {class: "nifty_form"} do |f| %>
  <%= f.text_field :path %>
  <%= f.text_area :caption, size: "60x12" %>
  <%= f.submit "Create" %>
<% end %>

<!-- HTML output -->
<form accept-charset="UTF-8" action="/photos/create" method="post" class="nifty_form">
  <input id="photos_path" name="photo[path]" type="text" />
  <textarea id="photos_caption" name="photo[caption]" cols="60" rows="12"></textarea>
  <input name="commit" type="submit" value="Create" />
</form>

Create a form with a custom action and method

<%= form_tag("/search", method: "get") do %>
  <%= label_tag(:q, "Search for:") %>
  <%= text_field_tag(:q) %>
  <%= submit_tag("Search") %>
<% end %>

<form accept-charset="UTF-8" action="/search" method="get">
  <input name="utf8" type="hidden" value="&#x2713;" />
  <label for="q">Search for:</label>
  <input id="q" name="q" type="text" />
  <input name="commit" type="submit" value="Search" />
</form>

Reference: http://guides.rubyonrails.org/form_helpers.html