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Ruby on Rails Cheatsheet

Ruby on Rails Cheatsheet


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


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'



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



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



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

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

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


Scaffolding is great for prototypes but don't rely too heavily on it:

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


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>


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 =
# 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" />

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" />


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It's really well summarized and helps me understand it well.
Thank you, Mike

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Great summary. Thanks.

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estherkimyunjung commented Jun 4, 2020 via email

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This helped me. Cheers.

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I love this so helpful.

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Perfect cheatsheet, thanks

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This is great!!!! Thank you sooooo much!

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great job! thanks.

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Cool. thanks bro

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Thank you my friend !!! from france. Mieux que ruby.doc ^_^

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P3nny commented Dec 3, 2020

Thanks, this helps.

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This is lovely. Thank you.

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aleiton commented Apr 20, 2021

Really helpful, thanks!

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Love this. Super helpful for review.

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devcamke commented Feb 4, 2022

Thank you please.
This is helpful, it makes it easy for beginners to understand the fundamental concepts of Ruby on Rails

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Thank you for this!

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Thank you soo much it helped me
keep postin good things

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really helpful...

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Pretty good for sharing.

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