Ruby on Rails Cheatsheet

Credit to mdang for creating much of this document.

Table of Contents

1. Architecture
2. Creating an Application
3. Routes
4. Controllers
5. Models
6. Migrations
7. Scaffolding
8. Rake
9. Path Helpers
10. Asset Pipeline
11. Form Helpers

Architecture

Creating an 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'

# The above is the same as: 
get :welcome, to: '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'
# and
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]

# Remember `resources :photos` from before? That's the same as:
resources :photos, only: [:index, :show, :new, :create, :edit, :update, :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

A killer Rails model cheatsheet: https://devhints.io/rails-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

Special block methods

• :timestamps - Creates created_at and updated_at datetime columns (i.e. t.timestamps, null: false)
• :index - Creates an index for the specified column (i.e. t.index :created_at)

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

Migration Creation Methods

• Standard
  • create_table
  • add_column
  • add_index
  • change_table
  • change_column
  • rename_table
  • rename_column
  • add_timestamps
• Advanced
  • create_join_table
  • add_foreign_key
  • add_reference

Migration Modification Methods

• Standard
  • change_table
  • change_column
  • rename_table
  • rename_column
  • rename_index
• Advanced
  • change_column_default
  • change_column_null

Migration Deletion Methods

• Standard
  • drop_table
  • remove_column
  • remove_columns
  • remove_index - By column name, i.e. remove_index :posts, :photo_id
  • remove_timestamps
• Advanced
  • drop_join_table
  • remove_foreign_key
  • remove_reference
  • remove_index - By index name, i.e. remove_index :posts, name: :index_posts_on_photo_id

Scaffolding

Scaffolding is great for prototypes but don't rely too heavily on it: http://stackoverflow.com/a/25140503. After an initial product launch, it's usually a good idea to manually create the files you need, avoiding scaffolding altogether.

$ 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 the following commands 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

Rollback a specific number of migrations. i.e. Rollback 5 times:

$ rake db:rollback STEP=5

Rollback any particular migration without affecting preceeding/proceeding migrations, where the version is the migration filename's timestamp prefix. i.e. Rollback 20170103201478_create_photos.rb:

$ rake db:migrate:down VERSION=20170103201478

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