This example assumes Ruby and Ruby on Rails have already been installed properly. If not, you can find how to do it here (opens new window).

Open up a command line or terminal. To generate a new rails application, use rails new (opens new window) command followed by the name of your application:

$ rails new my_app

If you want to create your Rails application with a specific Rails version then you can specify it at the time of generating the application. To do that, use rails _version_ new followed by the application name:

$ rails _4.2.0_ new my_app 

This will create a Rails application called MyApp in a my_app directory and install the gem dependencies that are already mentioned in Gemfile using bundle install.

To switch to your newly created app's directory, use the cd command, which stands for change directory.

$ cd my_app

The my_app directory has a number of auto-generated files and folders that make up the structure of a Rails application. Following is a list of files and folders that are created by default:

Now you need to create a database from your database.yml file:

rake db:create
# OR
rails db:create

rake db:create

Now that we've created the database, we need to run migrations to set up the tables:

rake db:migrate
# OR
rails db:migrate

rake db:migrate

To start the application, we need to fire up the server:

$ rails server
# OR
$ rails s

By default, rails will start the application at port 3000. To start the application with different port number, we need to fire up the server like,

$ rails s -p 3010

If you navigate to http://localhost:3000 (opens new window) in your browser, you will see a Rails welcome page, showing that your application is now running.

If it throws an error, there may be several possible problems:

• There is a problem with the config/database.yml
• You have dependencies in your Gemfile that have not been installed.
• You have pending migrations. Run rails db:migrate
• In case you move to the previous migration rails db:rollback

If that still throws an error, then you should check your config/database.yml

Rails uses sqlite3 as the default database, but you can generate a new rails application with a database of your choice. Just add the -d option followed by the name of the database.

$ rails new MyApp -T -d postgresql

This is a (non-exhaustive) list of available database options:

• mysql
• oracle
• postgresql
• sqlite3
• frontbase
• ibm_db
• sqlserver
• jdbcmysql
• jdbcsqlite3
• jdbcpostgresql
• jdbc

The -T command indicate to skip the installation of minitest. To install an alternative test suite like RSpec (opens new window), edit the Gemfile and add

group :development, :test do
  gem 'rspec-rails', 
end

Then launch the following command from the console:

rails generate rspec:install

To generate a controller (for example Posts), navigate to your project directory from a command line or terminal, and run:

$ rails generate controller Posts

You can shorten this code by replacing generate with g, for example:

$ rails g controller Posts

If you open up the newly generated app/controllers/posts_controller.rb you'll see a controller with no actions:

class PostsController < ApplicationController
    # empty
end

It's possible to create default methods for the controller by passing in controller name arguments.

$ rails g controller ControllerName method1 method2

To create a controller within a module, specify the controller name as a path like parent_module/controller_name. For example:

$ rails generate controller CreditCards open debit credit close
# OR
$ rails g controller CreditCards open debit credit close

This will generate the following files:

Controller: app/controllers/credit_cards_controller.rb
Test:       test/controllers/credit_cards_controller_test.rb
Views:      app/views/credit_cards/debit.html.erb [...etc]
Helper:     app/helpers/credit_cards_helper.rb

A controller is simply a class that is defined to inherit from ApplicationController.

It's inside this class that you'll define methods that will become the actions for this controller.

Installing Rails on Ubuntu

On a clean ubuntu, installation of Rails should be straight forward

Upgrading ubuntu packages

sudo apt-get update
sudo apt-get upgrade

Install Ruby and Rails dependecies

sudo apt-get install git-core curl zlib1g-dev build-essential libssl-dev libreadline-dev libyaml-dev libsqlite3-dev sqlite3 libxml2-dev libxslt1-dev libcurl4-openssl-dev python-software-properties libffi-dev

Installing ruby version manager. In this case the easy one is using rbenv

git clone https://github.com/rbenv/rbenv.git ~/.rbenv
echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc
echo 'eval "$(rbenv init -)"' >> ~/.bashrc

Installing Ruby Build

git clone https://github.com/rbenv/ruby-build.git ~/.rbenv/plugins/ruby-build
echo 'export PATH="$HOME/.rbenv/plugins/ruby-build/bin:$PATH"' >> ~/.bashrc

Restart Shell

exec $SHELL

Install ruby

rbenv install 2.3.1
rbenv global 2.3.1
rbenv rehash

Installing rails

gem install rails

Installing Rails on Windows

Step 1: Installing Ruby

We need Ruby programming language installed. We can use a precompiled version of Ruby called RubyInstaller.

• Download and run Ruby Installer from rubyinstaller.org (opens new window).
• Run the installer. Check "Add Ruby executables to your PATH", then install.
• To access Ruby, go to the Windows menu, click All Programs, scroll down to Ruby, and click “Start Command Prompt with Ruby”. A command prompt terminal will open. If you type ruby -v and press Enter, you should see the Ruby version number that you installed.

Step 2: Ruby Development Kit

After installing Ruby, we can try to install Rails. But some of the libraries Rails depends on need some build tools in order to be compiled, and Windows lacks those tools by default. You can identify this if you see an error while attempting to install Rails Gem::InstallError: The ‘[gem name]’ native gem requires installed build tools. To fix this, we need to install the Ruby Development Kit.

• Download the DevKit (opens new window)
• Run the installer.
• We need to specify a folder where we’re going to permanently install the DevKit. I recommend installing it in the root of your hard drive, at C:\RubyDevKit. (Don’t use spaces in the directory name.)

Now we need to make the DevKit tools available to Ruby.

• In your command prompt, change to the DevKit directory. cd C:\RubyDevKit or whatever directory you installed it in.
• We need to run a Ruby script to initialize the DevKit setup. Type ruby dk.rb init. Now we’ll tell that same script to add the DevKit to our Ruby installation. Type ruby dk.rb install.

The DevKit should now be available for your Ruby tools to use when installing new libraries.

Step 3: Rails

Now we can install Rails. Rails comes as a Ruby gem. In your command prompt, type:

gem install rails

Once you press Enter, the gem program will download and install that version of the Rails gem, along with all the other gems Rails depends on.

Step 4: Node.js

Some libraries that Rails depends on require a JavaScript runtime to be installed. Let’s install Node.js so that those libraries work properly.

• Download the Node.js installer from here (opens new window).
• When the download completes, visit your downloads folder, and run the node-v4.4.7.pkg installer.
• Read the full license agreement, accept the terms, and click Next through the rest of the wizard, leaving everything at the default.
• A window may pop up asking if you want to allow the app to make changes to your computer. Click “Yes”.
• When the installation is complete, you’ll need to restart your computer so Rails can access Node.js.

Once your computer restarts, don’t forget to go to the Windows menu, click “All Programs”, scroll down to Ruby, and click “Start Command Prompt with Ruby”.

Rails is shipped by default with ActiveRecord, an ORM (Object Relational Mapping) derived from the pattern with the same name (opens new window).

As an ORM, it is built to handle relational-mapping, and more precisely by handling SQL requests for you, hence the limitation to SQL databases only.

However, you can still create a Rails app with another database management system:

1. simply create your app without active-record

$ rails app new MyApp --skip-active-record

1. add your own database management system in Gemfile

gem 'mongoid', '~> 5.0'

1. bundle install and follow the installation steps from the desired database.

In this example, mongoid is an object mapping for MongoDB and - as many other database gems built for rails - it also inherits from ActiveModel the same way as ActiveRecord, which provides a common interface for many features such as validations, callbacks, translations, etc.

Other database adapters include, but are not limited to :

This example assumes that you have experience in creating Rails applications.

To create an API-only app in Rails 5, run

rails new name-of-app --api

Add active_model_serializers in Gemfile

gem 'active_model_serializers'

install bundle in terminal

bundle install

Set the ActiveModelSerializer adapter to use :json_api

# config/initializers/active_model_serializer.rb
ActiveModelSerializers.config.adapter = :json_api
Mime::Type.register "application/json", :json, %w( text/x-json application/jsonrequest application/vnd.api+json )

Generate a new scaffold for your resource

rails generate scaffold Task name:string description:text

This will generate the following files:

Controller: app/controllers/tasks_controller.rb

Test:       test/models/task_test.rb
            test/controllers/tasks_controller_test.rb
Routes:     resources :tasks added in routes.rb
Migration:  db/migrate/_create_tasks.rb
Model:      app/models/task.rb
Serializer: app/serializers/task_serializer.rb
Controller: app/controllers/tasks_controller.rb

From guides.rubyonrails.org:

Instead of generating a model directly . . . let's set up a scaffold. A scaffold in Rails is a full set of model, database migration for that model, controller to manipulate it, views to view and manipulate the data, and a test suite for each of the above.

Here's an example of scaffolding a resource called Task with a string name and a text description:

rails generate scaffold Task name:string description:text

This will generate the following files:

Controller: app/controllers/tasks_controller.rb
Test:       test/models/task_test.rb
            test/controllers/tasks_controller_test.rb
Routes:     resources :tasks added in routes.rb
Views:      app/views/tasks
            app/views/tasks/index.html.erb
            app/views/tasks/edit.html.erb
            app/views/tasks/show.html.erb
            app/views/tasks/new.html.erb
            app/views/tasks/_form.html.erb
Helper:     app/helpers/tasks_helper.rb
JS:         app/assets/javascripts/tasks.coffee 
CSS:        app/assets/stylesheets/tasks.scss
            app/assets/stylesheets/scaffolds.scss

example to delete files generated by scaffold for the resource called Task

rails destroy scaffold Task

Remarks

(opens new window)

Ruby on Rails (RoR), or Rails, is an open-source popular web application framework. Rails uses Ruby, HTML, CSS, and JavaScript to create a web application that runs on a web server. Rails uses the model-view-controller (MVC) pattern and provides a fullstack of libraries from the database all the way to the view.