Update Gemfile

# update gem 'rails', '~> 5.2.2.1' to
gem 'rails', '~> 6.0.0'

# add
gem 'webpacker', '~> 4.0'

Grab updates & install webpack

bundle update

bin/rails webpacker:install

Run your test and fix any issues. I mostly got issues revolving around update_attributes and expanding where.not() queries.

I had to update a bunch of
@resource.update_attributes(resource_params)
to
@resource.update(resource_params).

I also had scopes that looked like:

scope :complete, -> { where.not(resume_id: nil, cover_letter_id: nil, company_id: nil) }

They had to be updated to:

scope :complete, -> { where.not(resume_id: nil).where.not(cover_letter_id: nil).where.not(company_id: nil) }

Also, I had an issue with one of my render partials.

Failure/Error: <%= render partial: :company_datum, collection: @company_data, locals: { offset: @company_data.offset }, cached: true %>

Had to update it to:

<%= render partial: 'company_datum', collection: @company_data, locals: { offset: @company_data.offset }, cached: true %>

Updating application.rb

# config/application.rb
# change config.load_defaults 5.2
config.load_defaults 6.0

# I removed
config.i18n.fallbacks = [I18n.default_locale]

If using rubocop: add this to your .rubocop.yml

AllCops:
  Exclude:
    - 'node_modules/**/*'
...

Fin.