A basic overview of Ruby on Rails main components and how they work together.

Environment and Console

The console is based in irb (Interactive Ruby) and it can be accessed with rails console:

$ rails console --help
Running via Spring preloader in process 18521
Usage: rails console [environment] [options]
-s, --sandbox Rollback database modifications on exit.
-e, --environment=name Specifies the environment to run this console under (test/development/production).
Default: development

Rails comes with three environments:

  • development (started by default in the console)
  • test
  • production

These environments can be specified in the console, or by setting the RAILS_ENV variable like: RAILS_ENV=production. Then the environment can be accessed in the code with the env attribute of the Rails object: Rails.env

Sandbox console

It is possible to test the app in the console without changing the database running a sandboxed instance with rails console--sandbox:

$ rails console --sandbox
Running via Spring preloader in process 3485
Loading development environment in sandbox (Rails 5.0.0)
Any modifications you make will be rolled back on exit


Routes are defined in /config/routes.rb. After starting the server rails serve the current routes that rails recognizes can be listed at: http://localhost:3000/rails/info/routes in the browser or in the console: rails routes

Named routes

Defining a route in /config/routes.rb like:

Rails.application.routes.draw do
  get 'contact', to: 'pages#contact'

makes several named routes variables available, like contact_path and contact_url so they can be used in other files, e.g:

  test "should get contact" do
    get contact_path
    assert_response :success

In this case, these routes are contact_path and contact_url, the difference between them is that _url includes the full URL:

contact_path -> '/contact'
contact_url  -> 'http://www.example.com/contact'

The common convention is to use the _path form except when doing redirects, where _url form is preferred because the HTTP standard requires a full URL after redirects.

A custom name for a route, instead of the default one, can also be specified with the as keyword:

  get 'contact', to: 'pages#contact'`, as: 'other-contact'

Web Request Handling

Web requests are handled by

Rails applications favors the conventions of the REST architecture, it makes it easy to represent data as resources that respond to the four actions corresponding to the four fundamental operations POST, GET, PATCH, and DELETE of the HTTP standard:

  • create
  • show
  • update
  • destroy

For example, to create a RESTful User resource in config/routes.rb with resources :users generates all this routes:

Resource routes

Helper HTTP Verb Path Controller#Action
root_path GET / pages#home
users_path GET /users(.:format) users#index
  POST /users(.:format) users#create
new_user_path GET /users/new(.:format) users#new
edit_user_path GET /users/:id/edit(.:format) users#edit
user_path GET /users/:id(.:format) users#show
  PATCH /users/:id(.:format) users#update
  PUT /users/:id(.:format) users#update
  DELETE /users/:id(.:format) users#destroy

To simulate a PATCH request, Rails sets an input hidden field in forms like <input ... value="patch" /> so web browsers can send it; the original HTML forms specification didn’t include them.


$ rails generate model User username:string email:string
Running via Spring preloader in process 28981
      invoke  active_record
      create    db/migrate/20160810191131_create_users.rb
      create    app/models/user.rb
      invoke    test_unit
      create      test/models/user_test.rb
      create      test/fixtures/users.yml




Templates can be .erb, builder or JBuilder templates


ERB stands for Embedded Ruby files (ruby tags mixed with HTML).

ERB templates are written in .erb files.

They are located in app/views directory.

Ruby code can be included using the tags:

  • <% %> used for conditions, loops or blocks
  • <%= %> outputs content


Partials templates are parts of a template that can be reused and located in different files for better structuring the app.

To render a partial with render method:

  • file: _comment.html gets rendered with:
<%= render "comment" %>
  • file: app/views/shared/_comment.html.erb with:
<%= render "shared/comment" %>

<%= render partial: "product", locals: { product: @product } %> can be called as: <%= render "product", product: @product %>

Forms from Models

When building a form using form_for and a model name (form_for(@foo)), Rails decides which type of request to use based in:

  • if @foo.new_record? == true uses POST.
  • if @foo.new_record? == false uses PATCH.

Asset pipeline

The assets pipeline makes it easier to produce and manage static assets such as

  • CSS
  • JavaScript
  • images

The asset pipeline provides a framework to concatenate and minify or compress JavaScript and CSS assets. It also adds the ability to write these assets in other languages and pre-processors such as CoffeeScript, Sass and ERB. It allows assets in your application to be automatically combined with assets from other gems.

Ruby on rails Guides

Pipeline assets can be located in:

  • app/assets application assets, such as
    • custom images
    • JavaScript files
    • CSS
  • lib/assets own libraries
    • code that doesn’t fit into the scope of the application or
    • libraries which are shared across applications
  • vendor/assets assets owned by outside entities, such as
    • JavaScript plugins
    • CSS frameworks

All of them have manifest files app/assets/stylesheets/application.css to select how to process them and in what order.

Asset pipeline is handled in rails with Sprockets, the Rack-based asset packaging system https://github.com/sstephenson/sprockets.


Sessions in Rails are commonly implemented with cookies, there are two special method:

  • session to make temporary sessions (expire automatically on browser close)
  • cookies to make longer-lived sessions.

Having a cookie based authentication system, we can model sessions as RESTful resources:

  • login form -> handled by new action
  • logging in -> POST request to the__create__ action
  • logging out -> DELETE request to the destroy action


Integration tests

Testing how several components of the app interacts with integration tests:

$ rails generate integration_test SiteLayout
Running via Spring preloader in process 9703
      invoke  test_unit
      create    test/integration/site_layout_test.rb

Main resources



Marcelo Canina
I'm Marcelo Canina, a developer from Uruguay. I build websites and web-based applications from the ground up and share what I learn here.