Upgrade Rails 4 into Rails 6

upgrade-rails-4-into-rails-6.md

How to upgrade Rails 4 into Rails 6? Step by Step

• It's recommended to set ruby into e.g v2.6.5 by creating .ruby_version (if your are using rbenv) and add ruby '2.6.5' in Gemfile

  # Gemfile
  source 'https://rubygems.org'
  
  ruby '2.6.5'

• Change Rails version

  # Gemfile
  - gem 'rails', '4.1.5'
  + gem 'rails', '~> 6.0.2', '>= 6.0.2.1'

• Upgrade Saas Rails

  # Gemfile
  - gem 'sass-rails', '~> 4.0.3'
  + gem 'sass-rails', '>= 6'

• Remove rubyracer if any, not needed

• Remove cofee-rails if any, or remove version tag

  # Gemfile
  - gem 'coffee-rails', '~> 4.0.0'
  + gem 'coffee-rails' # let bundler choose version for now
  - gem 'therubyracer',  platforms: :ruby

• Ruby bundle update and fix dependencies until running bundle without errors

• Run console rails c to check,

• If you get errors : Expected to find a manifest file in app/assets/config/manifest.js fix it by create those file

  # app/assets/config/manifest.js
  //= link_tree ../images
  //= link_directory ../javascripts .js
  //= link_directory ../stylesheets .css

• If you get error when migrate db rails db:migrate

  rails aborted!
  StandardError: An error has occurred, this and all later migrations canceled:
  
  Directly inheriting from ActiveRecord::Migration is not supported. Please specify the Rails release the migration was written for:
  
    class DeviseCreateUsers < ActiveRecord::Migration[4.1]
  /Users/gizipp/Code/pms/db/migrate/20140911020345_devise_create_users.rb:1:in <top (required)>

  simply change all migrations from ActiveRecord::Migration into with specified version e.g ActiveRecord::Migration[6.0][6.1] and try migrate again

• Add gem 'webpacker' in Gemfile

• Try run rails s, errors happen

  Webpacker configuration file not found /Users/gizipp/Code/pms/config/webpacker.yml. Please run rails webpacker:install Error: No such file or directory @ rb_sysopen - /Users/gizipp/Code/pms/config/webpacker.yml (RuntimeError)

then run `rails webpacker:install`

then change css js tag on `application.html.erb`

  ```ruby
  <%= stylesheet_pack_tag    'application' %>
  <%= javascript_pack_tag    'application' %>

MISC errors

• If error This Gemfile requires a different version of Bundler. try run gem install bundler
• If you using simple_form and got errors Use rails generate simple_form:install to generate the Simple Form configuration.