3.7 to 4.0

If you have any questions or suggestions feel free to reach out through Spree slack channels​
If you're on an older version than 3.7 please follow previous upgrade guides and perform those upgrades incrementally, eg.
1.​upgrade 3.2 to 3.3​
2.​upgrade 3.3 to 3.4​
3.​upgrade 3.4 to 3.5​
4.​upgrade 3.5 to 3.6​
5.​upgrade 3.6 to 3.7​
This is the safest and recommended method.
Update your Ruby version to 2.5.0 at least
Spree 4.0 requires Ruby 2.5.0 at least so you need to bump the ruby version in your project's Gemfile and .ruby-version files.
Migrate from Paperclip to ActiveStorage
In Spree 3.6 we deprecated Paperclip support in favor of ActiveStorage. Paperclip gem itself isn't maintained anymore and it is recommended to move to ActiveStorage as it is the default Rails storage engine since Rails 5.2 release.
In Spree 4.0 we've removed Paperclip support in favor of ActiveStorage.
Please remove also any occurrences of Rails.application.config.use_paperclip and Configuration::Paperclip from your codebase.
Please follow the official Paperclip to ActiveStorage migration guide.
Replace OrderContents with services in your codebase
OrderContents was deprecated in Spree 3.7 and removed in 4.0. We've replaced it with service objects.
You need to replace any instances of OrderContents usage with corresponding services in your codebase.
OrderContents#update_cart
before:
order.contents.update_cart(line_items_attributes)
after:
Spree::Cart::Update.call(order: order, params: line_items_attributes)
OrderContents#add
before:
order.contents.add(variant, quantity, shipment: shipment)
after:
Spree::Cart::AddItem.call(
  order: order,
  variant: variant,
  quantity: quantity,
  options: {
    shipment: @shipment
  }
)
OrderContents#remove
before:
order.contents.remove(variant, quantity, shipment: shipment)
after:
Spree::Cart::RemoveItem.call(
  order: order,
  variant: variant,
  quantity: quantity,
  options: {
    shipment: shipment
  }
)
Replace add_store_credit_payments with Checkout::AddStoreCredit
Similar to OrderContents method add_store_credit_payments was replaced with Checkout::AddStoreCredit service.
before:
order.add_store_credit_payments
after:
Spree::Checkout::AddStoreCredit.call(order: order)
Replace remove_store_credit_payments with Checkout::RemoveStoreCredit
Similar to OrderContents method remove_store_credit_payments was replaced with Checkout::RemeoveStoreCredit service.
before:
order.remove_store_credit_payments
after:
Spree::Checkout::RemoveStoreCredit.call(order: order)
Remove spree_address_book extension
If you're using the Address Book extension you need to remove it as this feature was merged into core Spree.
1.Remove this line from Gemfile
 gem 'spree_address_book', github: 'spree-contrib/spree_address_book'
2.Remove this line from vendor/assets/javascripts/spree/frontend/all.js
 //= require spree/frontend/spree_address_book
3.Remove this line from vendor/assets/stylesheets/spree/frontend/all.css
 //= require spree/frontend/spree_address_book
Replace class_eval with Module.prepend (only for Rails 6)
Rails 6.0 ships with a new code autoloader called Zeitwerk which has some strict rules in terms of file naming and contents. If you used class_eval to extend and modify Spree classes you will need to rewrite those with Module.prepend. Eg.
Old decorator syntax - app/models/spree/order_decorator.rb
Spree::Order.class_eval do
  has_many :new_custom_model
​
  def some_method
     # ...
  end
end
New decorator syntax - app/models/my_store/spree/order_decorator.rb
module MyStore
  module Spree
    module OrderDecorator
      def self.prepended(base)
        base.has_many :new_custom_model
      end
​
      def some_method
        # ...
      end
    end
  end
end
​
::Spree::Order.prepend(MyStore::Spree::OrderDecorator)
When migrating a class method to the new autoloader things are a little different because you will have to prepend to the Singleton class as shown in this example:
module Spree::BaseDecorator
  def spree_base_scopes
    # custom implementation
  end
end
​
Spree::Base.singleton_class.send :prepend, Spree::BaseDecorator
Please also consider other options for Logic Customization.
We recommend also reading through Ruby modules: Include vs Prepend vs Extend​
Update Bootstrap 3 to 4 or stay at Bootstrap 3
Spree 4 uses Bootstrap 4 for both Storefront and Admin Panel. You have two options:
Stay at Bootstrap 3
As we know this is a big portion of work you can still use Bootstrap 3 for your Storefront.
1.Copy all remaining views by running bundle exec spree:frontend:copy_views
2.Add bootstrap-sass gem to your Gemfile
 gem 'bootstrap-sass', '~> 3.4.1'
Move to Bootstrap 4
​Follow the official Bootstrap 3 to 4 migration guide​
Update Gemfile
gem 'spree', '~> 4.0'
gem 'spree_auth_devise', '~> 4.0'
gem 'spree_gateway', '~> 3.6'
Run bundle update
Install missing migrations
rails spree:install:migrations
rails spree_api:install:migrations
rails spree_auth:install:migrations
rails spree_gateway:install:migrations
Run migrations
rails db:migrate
Read the release notes
For information about changes contained within this release, please read the 4.0.0 Release Notes.
More info
If you have any questions or suggestions feel free to reach out through Spree slack channels​