A step by step guide to upgrade rails 4 application to rails 5

Upgrading an application can be tedious if you don’t have good test coverage.

This article covers the common issues you might face while upgrading the from rails 4 to 5.

If you are upgrading to ruby 2.7 export RUBYOPT="-W0" to avoid getting your screen filled up with deprecations warnings

export RUBYOPT="-W0"

bundle exec rspec

# OR use

RUBYOPT="-W0" bundle exec rspec

Step 1: Upgrading ruby and bundle install

• Install the required ruby version

  • rvm

    rvm install ruby 2.x.x
    

  • rbenv

    rbenv install 2.x.x
    

• Change the ruby version in .ruby-version, .rvmrc or Gemfile.

• Install bundler

  gem install bundler
  

• Change the rails version

  # Gemfile
  gem 'rails', '4.2.0'
  # To
  gem 'rails', '5.2.4'
  

• run bundle install

  If you don’t need specific versions of the gems locked it is better to remove the specified version.

  bundle install
  

• Additional Note: (ruby 2.7)

  Ruby 2.7 has removed these gems which were default in prior versions.

  Add the following gems to your gemfile

  gem 'e2mmap'
  gem 'scanf'
  gem 'thwait'
  

Step 2: Config changes

At this point you should be able to install all the dependencies. But, in order to start the application we need to do some config changes.

• Remove

  # config/application.rb
  config.active_record.raise_in_transactional_callbacks = true
  

• Change

  # config/application.rb
  config.serve_static_assets = true
  # or
  config.serve_static_files = true
  
  # to
  config.public_file_server.enabled
  

  # config/application.rb
  config.static_cache_control = 'public, max-age=3600'
  
  #to
  
  config.public_file_server.headers = { 'Cache-Control' => 'public, max-age=3600' }
  

  # routes.rb
  ProjectName::Application.routes.draw do
  
  # to
  
  Rails.application.routes.draw do
  

• Create config/initializers/assets.rb

  # config/initializers/assets.rb
  Rails.application.config.assets.version = '1.0'
  
  Rails.application.config.assets.precompile += [
    'application.css', 'application.js'
  ]
  

Step 3: Model & Controller changes

Controllers

• Replace all *_filter callbacks in favor of *_action

  before_filter
  skip_before_filter
  
  # to
  
  before_action
  skip_before_action
  

  redirect_to(:back)
  
  # to
  
  redirect_back(fallback_location: root_path)
  

Models

• Models now inherit from ApplicationRecord

  • Create

    # app/models/application_record.rb
    class ApplicationRecord < ActiveRecord::Base
      self.abstract_class = true
    end
    

  • Change the following in all models

    class User < ActiveRecord::Base
    
    # to
    
    class User < ApplicationRecord
    

• belongs_to is compulsory now.

  Use optional: true if the association is ever going to be nil

  class Post < ActiveRecord::Base
    belongs_to :user, optional: true
    #....
  

  In a huge application you might want to keep the old behavior. You can change the settings globally in application.rb

  # config/application.rb
  config.active_record.belongs_to_required_by_default = false
  

  after_destroy :send_confirmation, if: 'user&.notifications_enabled?'
  
  after_destroy :send_confirmation, if: Proc.new { user&.notifications_enabled? }
  

• attribute_changed? is deprecated in after_save callback

  Deprecated: _changed? doesn't work as expected in after_save & after_update
  Use saved_change_to_?

  # Old
  after_save :send_email, if: :email_changed?
  
  # New
  after_save :send_email, if: -> { saved_change_to_email? }
  

  Deprecated: _was doesn't work as expected in after_save & after_update
  Use _before_last_save

  # Old
  archived_record.assign_attributes(email: email_was)
  
  # New
  archived_record.assign_attributes(email: email_before_last_save)
  

• AASM if you’re upgrading aasm from 3 -> 4

  Follow this guide - Upgrading AASM from version 3 to 4

Mailers

• Mailers now inherit from ApplicationMailer

  # app/mailers/application_mailer.rb
  class ApplicationMailer < ActionMailer::Base
    default from: "sample@#{ActionMailer::Base.smtp_settings[:domain]}"
  end
  

  class UserMailer < ActionMailer::Base
  # to
  class UserMailer < ApplicationMailer
  

Step 4: Migration changes

Directly inheriting from ActiveRecord::Migration is not supported.
Please specify the Rails release the migration was written for:

• Change the following

  class CreateUsers < ActiveRecord::Migration
  
  # to
  
  class CreateUsers < ActiveRecord::Migration[4.2]
  

  Easy fix

  grep -rl "ActiveRecord::Migration$" db | xargs sed -i "s/ActiveRecord::Migration/ActiveRecord::Migration[4.2]/g"
  

Step 5: Necessary changes in RSpec

RSpec

• Upgrading FactoryBot to 5

  DEPRECATION WARNING: Static attributes will be removed in FactoryBot 5.0.
  Please use dynamic attributes instead by wrapping the attribute value in a block:

  FactoryBot.define do
    factory :user do
      name 'John'         # Bad & will throw error
      # To
      name { 'John' }     # Good
  

  Easy Fix:

  use rubocop to auto fix the format

  Ref: https://thoughtbot.com/blog/deprecating-static-attributes-in-factory_bot-4-11

  rubocop -a spec/factories/xyz.rb --only FactoryBot/AttributeDefinedStatically
  

  Make sure to comment the following in rubocop.yml temporarily

  AllCops:
    Exclude:
      - 'spec/**/*'
  

• Fix controller specs

  get :show, id: request.id
  xhr :get, :summary, id: request.id
  
  # to
  
  get :show, params: { id: request.id }
  get :summary, params: { id: request.id }, xhr: true
  

  This gem does it for you - rails5-spec-converter

Additional Issues you might get while running RSpec

• undefined method ‘sort’ for #<ActionController::Parameters:>

  Do not use Hash methods on params