Category Archives: Ruby

Ruby Inheritance Rules Simplified

A simple principle to understand Ruby inheritance is LIFO (Last In First Out).


  1. Ruby will search the object you’re calling it from
  2. It will search it in any included modules, starting with the last loaded module
  3. It will go in the superclass (technically, modules get in the inheritance hierarchy as well, but whatever)

When the method is found, the search stops.


A Note About Calling super.
The same rule applies if you use super. If you have the same method defined in both module and a parent class, the module method will be called.
Here’s a simple example:

module Test
  def abc
    puts 'abc from Module'

class TestClassParent
  def abc
    puts 'abc from parent'

class TestClassChild < TestClassParent
  include Test

  def abc

Running this will result in:

abc from Module

Debugging Rails

Install pry, pry-byebug, and pry-rails gems.
To add a breakpoint, type binding.pry wherever you want your breakpoint to happen.
In console use coninue, step, next, finish commands:

step: Step execution into the next line or method. Takes an optional numeric argument to step multiple times.

next: Step over to the next line within the same frame. Also takes an optional numeric argument to step multiple lines.

finish: Execute until current stack frame returns.

continue: Continue program execution and end the Pry session.

To add shortcuts to ^ commands, add to ~/.pryrc:
Pry.commands.alias_command ‘c’, ‘continue’ rescue nil
Pry.commands.alias_command ‘s’, ‘step’ rescue nil
Pry.commands.alias_command ‘n’, ‘next’ rescue nil
Pry.commands.alias_command ‘f’, ‘finish’ rescue nil

Starting with RSpec in Rails

Add RSpec related gems to gemfile:

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

group :test do
  gem "capybara"

Capybara is a framework for testing web applications; allows to navigate your app programmatically.

Install your RSpec gems: bundle install

Generate RSpec templates:
generate rspec: rails g rspec:install

To view all available generators: rails g

Since RSpec uses test database, run your migrations for test environment:
rails db:migrate RAILS_ENV=test
If this is the first run, may need to set up the database by running RAILS_ENV=test rake db:reset

To run all specs: rspec
To add formatting: rspec -format doc (or use shortcut: rspec -f doc)
To always use the same formatting, add -format doc to .rspec file.

To use helper files for RSpecs
Uncomment this line in rails_helper.rb:
Dir[Rails.root.join(‘spec/support/**/*.rb’)].each { |f| require f }
And place all your helper methods inside of spec/support directory.

Sample RSpec file:

require 'rails_helper'

describe 'Navigating movies' do
  it 'allows navigation from the detail page to the listing page' do
    movie = Movie.create(movie_attributes)

    visit movie_url(movie)

    click_link 'All Movies'

    expect(current_path).to eq(root_path)

Starting with Rails

Install Ruby. If you are on Windows, 2.3 seems to have issue as of September 2016, so I would go with 2.2.

Install Rails:
gem install rails –version 5.0.0 –no-ri –no-rdoc

Create a new application:
rails _5.0.0_ new application_name
use –skip-test or -T if you don’t want default test files or want to use a different test framework (Test::Unit is default)

Run the application:
rails s

If you are seeing something like this:

Could not load 'active_record/connection_adapters/sqlite3_adapter'. Make sure that the adapter in config/database.yml is valid. If you use an adapter other than 'mysql2', 'postgresql' or 'sqlite3' add the necessary adapter gem to the Gemfile.

You probably have ruby version above 2.2 and you are on Windows. Downgrade to 2.2 or try a different OS.

Create a route for your first action:

verb "url" => "name_of_controller#name_of_action"
get 'movies' => 'movies#index'

Generate/destroy a controller:

rails g controller name_of_controller
rails destroy controller name_of_controller

If you don’t want to use the default framework, add –no-test-framework when generating a controller.

Update your view with something like this:

<% @movies.each do |movie| %>

<li> <strong><%= movie.title %></strong> (<%= movie.rating %>) <%= number_to_currency(movie.total_gross) %></li>
<% end %>

Create a model

rails generate model NAME [field[:type][:index] field[:type]
rails g model event name:string location:string price:decimal

To generate the whole resource:

rails g resource Resource_name column_name:column_type --no-test-framework

To destroy the resource:

rails destroy resource Resource_name column_name:column_type --no-test-framework

Use any of these DB column types types for your model:


To declare foreign key relationship: belongs_to :parent
To reference children in parent model: has_many :children
To cascade deletes: has_many :reviews, dependent: :destroy

To attach parent to child: child.parent = parent

Run migration:
rails db:migrate
rauks db:migrate:status

Use seeds.rb to create seed records for development
To run: rails db:seed

To look up commands:
rails -T
rails -T db

To Look up routes:
rails routes
In browser: {your_app_base_address}/rails/info/routes

for path/url use route_name_path/route_name_url
In rails command line (rails c):
<%= link_to("Whatever text", route_name_path) %>
Shortcut: <%= link_to("Whatever text", model) %>
Use _path in view templates and _url in controllers as redirects.

Routes with parameters
get ‘route/:id’ => ‘controller#show’, as: ‘some_route_name’
<%= link_to "Whatever text", route_name_path(model) %>
Shortcut: <%= link_to "Whatever text", model %>

Root route
root ‘controller#action’

Submitting Forms
Sample form:

<%= form_for(@movie, @review) do |f| %>
    <%= f.label :title %>
    <%= f.text_field :title %>
  <% Review::STARS.each do |star| %>
    <%= f.radio_button :stars, star %> <%= star %>
  <% end %>
    <%= f.submit %>
<% end %>

Updating a model

def update
  @movie = Movie.find(params[:id])

To allow specific model fields to be updated
params[:movie].permit(:title, :description)

Or (will fail if movie is not submitted)

To allow all fields to be updated:

Working with Active Record
Movie.order(‘released_on asc’)
Movie.order(released_on: :asc)

Movie.find_by(title: “Iron Man”)
Movie.where(rating: “PG-13”)
Movie.where.not(rating: “PG-13”)
Movie.where.not(rating: [“PG”, “PG-13”])
Movie.where(“total_gross < ?", 50000000) Movie.where("released_on > ?”,
Movie.where(“released_on <= ?","released_on desc") To view SQL use to_sql: Movie.where(rating: "PG-13").to_sql To rollback last migration: rails db:rollback
To see assets: http://base_url/assets/asset_name

Active Record methods on an instance:

Validation Examples:
validates :title, :released_on, :duration, presence: true
validates :description, length: { minimum: 25 }
validates :total_gross, numericality: { greater_than_or_equal_to: 0 }

validates :image_file_name, allow_blank: true, format: {
with: /\w+\.(gif|jpg|png)\z/i,
message: “must reference a GIF, JPG, or PNG image”
RATINGS = %w(G PG PG-13 R NC-17)
validates :rating, inclusion: { in: RATINGS }

To run something before each action:
before_action :method_name

One time messages.
To set:
flash[:notice] = “Message!”
If in redirect, can do:
redirect_to some_url, alert: “Alert!”
To read in view:
<%= flash[:notice] %>

Custom Flashes with redirects:
Rails only supports :notice and :alert by default for redirects. To add a custom one, add this to your ApplicationController: add_flash_types(:danger)

To set gems for specific environment:
group :development, :test do
gem ‘sqlite3’
To install gems excluding a group:
bundle install –without production

Nested resources
resources :parents do
resources :children

Setting up Ruby with Sublime

Install Ruby (through Chocolatey or or whatever else if you’re on Windows)

Install a couple Sublime plugins:

  • Linting: SublimeLinter + SublimeLinter-Ruby + SublimeLinter-rubocop (see docs for RuboCop on
  • Rubocop gem (if isung RuboCop) – “gem install rubocop”
  • GitGutter (if you use git)
  • AllAutocomplete
  • BeautifyRuby – requires HTML Beautifier gem (gem install htmlbeautifier)

Update some preferences (Preferences – Settings):

"auto_complete": true,
"auto_complete_commit_on_tab": true,
"copy_with_empty_selection": true,
"ensure_newline_at_eof_on_save": true,
"font_size": 11,
"index_files": true,
"tab_size": 2,
"translate_tabs_to_spaces": true,
"trim_trailing_white_space_on_save": true,
"word_separators": "./\\()\"'-:,.;<>[email protected]#$%^&*|+=[]{}`~"

Some great recommendations on