Ruby On Rails


  1. Getting Start with Rails
  2. HTTP Requests in Rails Apps
  3. Action Controlller Overview


rails new [app] # scaffold new app rails server # serve on 3000 bundle install --without production # install dev deps rails generate scaffold User name:string email:string # generate basic User schema rails generate controller Welcome index # generate new Welcome page rails destroy model User # rollback created User rails db:migrate # migrate database rails db:rollback # undo previous db command rails db:migrate VERSION=0 # migrate all the way back to the beginning


  • rake = Ruby Make
  • rake used extensively before Rails 5
  • rails db:migrate === bundle exec rake db:migrate


sudo gem install rails (-v 2.3.8)

Or use rvm or asdf. Follow those instructions from their respective sites.

Up and Running

rails new [project-name] cd [project-name] bundle install # may need to `bundle update` rails server # start the server on port 3000

Hello World

rails new hello-world cd hello-world rails server # start server on port 3000

To change our default page, we can update the application controller and config/routes.rb file.

# app/controllers/application_controller class ApplicationController < ActionController::Base def hello render html: "Hello, world!" end end # config/routes.rb Rails.application.routes.draw do # For details on the DSL available within this file, see http://guides.rubyonrails.org/routing.html root 'application#hello' end

Now if we refresh the page, we should get a basic "Hello, world!" string!

Generating A Schema

rails generate scaffold User name:string email:string # generate basic User schema

Migrating New Schemas To A Database

rails db:migrate # for older versions bundle exec rake db:migrate

CRUD Operations For The Records

/usersindexList all users
/users/1showPage to show user with ID 1
/users/newnewPage to make a new user
/users/1/editeditPage to edit user with ID 1

Setting /users to root

# config/routes.rb Rails.application.routes.draw do resources :users # For details on the DSL available within this file, see http://guides.rubyonrails.org/routing.html root 'users#index' end

A Generated Controller

class UsersController < ApplicationController # ... # GET /users # GET /users.json def index @users = User.all end # ... end

The @users = User.all fetches all users from the database and stores them in the variable @users.


Using the generated data models, we can set validations and relationships.

class Micropost < ApplicationRecord validates :content, length: {maximum: 140}, presence: true belongs_to :user end class User < ApplicationRecord has_many :microposts validates :content, length: {maximum: 140} end

Building Static Pages

> rails generate controller StaticPages home help Running via Spring preloader in process 53372 create app/controllers/static_pages_controller.rb route get 'static_pages/home' get 'static_pages/help' invoke erb create app/views/static_pages create app/views/static_pages/home.html.erb create app/views/static_pages/help.html.erb invoke test_unit create test/controllers/static_pages_controller_test.rb invoke helper create app/helpers/static_pages_helper.rb invoke test_unit invoke assets invoke coffee create app/assets/javascripts/static_pages.coffee invoke scss create app/assets/stylesheets/static_pages.scss

This will build a StaticPages controller and pages home and help.

Build that controller using StaticPages would also work if we used the snake case version static_pages.

We can undo things by running rails destroy controller StaticPages home help.

After the pages are generated, we can see it has been added to to our config/routes.db file:

Rails.application.routes.draw do get 'static_pages/home' get 'static_pages/help' # ... rest omitted for brevity end

Understanding How Static Pages Work

We can find the logic for our controller coming from app/controllers/static_pages_controller.rb:

class StaticPagesController < ApplicationController def home end def help end end

While these methods in Ruby wouldn't do much, the story is different for Rails. First of all, notice that our Controller inherits from the ApplicationController. Rails looks in the Static Pages controller for the URL /static_pages/home, executes the code in the home method and then renders the view.

Given the home action is empty, all the visit to the URL mentioned prior does is render the view.

Updating The Test Helper

If you update test/test_helper.rb and update the lines post-last require to include the following, you can use the Minitest Reporter:

# ... omitted require "minitest/reporters" Minitest::Reporters.use! # ... omitted

Automating The Running Of Tests

We can use Guard to do this for us in an equivalent to watch mode!

bundle exec guard init

For the sake of Git, it is recommended to add the guard/ folder into .gitignore.

Model Relationships

In Ruby, we can model relationships using the following:

rails generate model Relationship follower_id:integer followed_id:integer

Adding An Index To DB Schemas

Assuming we created the relationship in the above section, we could update the file db/migrate/[timestamp]_create_relationships.rb for indexes:

class CreateRelationships < ActiveRecord::Migration[5.0] def change create_table :relationships do |t| t.integer :follower_id t.integer :followed_id t.timestamps end # For the indexes add_index :relationships, :follower_id add_index :relationships, :followed_id add_index :relationships, [:follower_id, :followed_id], unique: true end end

Re-running rails db:migrate will update the relationships for the database.

Implementing The Has-Many Relationship

For the example of User, we can update app/models/user.rb to have the following:

# Note: dependent: :destory will remove relationships when the entity is destroyed class User < ApplicationRecord has_many :microposts, dependent: :destroy has_many :active_relationships, class_name: "Relationships", foreign_key: "follower_id", dependent: :destroy end