> ## Documentation Index
> Fetch the complete documentation index at: https://spreecommerce.org/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# 3.7 to 4.0

> This guide covers upgrading a 3.7 Spree application to Spree 4.0.

<Note>
  If you're on an older version than 3.7 please follow previous upgrade guides and perform those upgrades incrementally\*\*, eg.

  1. [upgrade 3.4 to 3.5](3.4-to-3.5)
  2. [upgrade 3.5 to 3.6](3.5-to-3.6)
  3. [upgrade 3.6 to 3.7](3.6-to-3.7)
</Note>

## Update your Ruby version to 2.5 or later

Spree 4.0 requires Ruby 2.5 so you need to change the ruby version in your project's `Gemfile` and `.ruby-version` files. And of course you need to install Ruby 2.5 or later. If you're using RVM you can do it like this:

```bash theme={"theme":"night-owl"}
rvm install 2.5
rvm use 2.5
```

## Migrate from Paperclip to ActiveStorage

In Spree 3.6 we deprecated [Paperclip support in favor of ActiveStorage](https://guides.spreecommerce.org/release_notes/3_6_0.html#active-storage-support). 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](https://github.com/thoughtbot/paperclip/blob/master/MIGRATING).

## Remove `spree_address_book` extension

If you're using the [Address Book](https://github.com/spree-contrib/spree_address_book) extension you need to remove it as this feature was merged into [core Spree](https://github.com/spree/spree/releases/tag/v4.0.0).

1. Remove this line from `Gemfile`

   ```bash theme={"theme":"night-owl"}
   bundle remove spree_address_book
   ```

2. Remove this line from `vendor/assets/javascripts/spree/frontend/all.js`

   ```text theme={"theme":"night-owl"}
    //= require spree/frontend/spree_address_book
   ```

3. Remove this line from `vendor/assets/stylesheets/spree/frontend/all.css`

   ```text theme={"theme":"night-owl"}
    //= require spree/frontend/spree_address_book
   ```

## Update your `Gemfile`

```ruby theme={"theme":"night-owl"}
gem 'spree', '~> 4.0'
gem 'spree_auth_devise', '~> 4.0'
gem 'spree_gateway', '~> 3.6'
```

and run

```bash theme={"theme":"night-owl"}
bundle update
```

## Replace `class_eval` with `Module.prepend` only for Rails 6

Rails 6.0 ships with a [new code autoloader called Zeitwerk](https://medium.com/@fxn/zeitwerk-a-new-code-loader-for-ruby-ae7895977e73) which has some [strict rules in terms of file naming and contents](https://github.com/fxn/zeitwerk#file-structure). If you used `class_eval` to extend and modify Spree classes you will need to rewrite those with `Module.prepend`. Eg.

Old decorator syntax:

```ruby theme={"theme":"night-owl"}
Spree::Order.class_eval do
  has_many :new_custom_model

  def some_method
     # ...
  end
end
```

Replaced with:

```ruby theme={"theme":"night-owl"}
module Spree
  module OrderDecorator
    def self.prepended(base)
      base.has_many :new_custom_model
    end

    def some_method
      # ...
    end
  end

  Order.prepend(OrderDecorator)
end
```

When migrating a class method to the new [autoloader](https://medium.com/@fxn/zeitwerk-a-new-code-loader-for-ruby-ae7895977e73) things are a little different because you will have to prepend to the Singleton class as shown in this example:

```ruby theme={"theme":"night-owl"}
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](/developer/customization).

We recommend also reading through [Ruby modules: Include vs Prepend vs Extend](https://medium.com/@leo_hetsch/ruby-modules-include-vs-prepend-vs-extend-f09837a5b073)

## 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`

   ```ruby theme={"theme":"night-owl"}
    gem 'bootstrap-sass', '~> 3.4.1'
   ```

### Move to Bootstrap 4

[Follow the official Bootstrap 3 to 4 migration guide](https://getbootstrap.com/docs/4.0/migration/)

## Install missing migrations

```bash theme={"theme":"night-owl"}
rake railties:install:migrations
```

## Run migrations

```bash theme={"theme":"night-owl"}
rails db:migrate
```

## Read the release notes

For information about changes contained within this release, please read the [4.0.0 Release Notes](https://github.com/spree/spree/releases/tag/v4.0.0)