Active Storage makes it simple to upload and reference files in cloud services, like Amazon S3 or Google Cloud Storage, and attach those files to Active Records. It also provides a disk service for testing or local deployments, but the focus is on cloud storage.

A key difference to how Active Storage works compared to other attachment solutions in Rails is through the use of built-in Blob and Attachment models (backed by Active Record). This means existing application models do not need to be modified with additional columns to associate with files. Active Storage uses GlobalID to provide polymorphic associations via the join model of Attachment, which then connects to the actual Blob.

These Blob models are intended to be immutable in spirit. One file, one blob. You can associate the same blob with multiple application models as well. And if you want to do transformations of a given Blob, the idea is that you'll simply create a new one, rather than attempt to mutate the existing (though of course you can delete that later if you don't need it).

One attachment:

class User < ApplicationRecord
  has_one_attached :avatar
end

user.avatar.attach io: File.open("~/face.jpg"), filename: "avatar.jpg", content_type: "image/jpg"
user.avatar.exist? # => true

user.avatar.purge
user.avatar.exist? # => false

user.avatar.url(expires_in: 5.minutes) # => /rails/blobs/<encoded-key>

class AvatarsController < ApplicationController
  def update
    Current.user.avatar.attach(params.require(:avatar))
    redirect_to Current.user
  end
end

Many attachments:

class Message < ApplicationRecord
  has_many_attached :images
end

<%= form_with model: @message do |form| %>
  <%= form.text_field :title, placeholder: "Title" %><br>
  <%= form.text_area :content %><br><br>

  <%= form.file_field :images, multiple: true %><br>
  <%= form.submit %>
<% end %>

class MessagesController < ApplicationController
  def create
    message = Message.create! params.require(:message).permit(:title, :content)
    message.images.attach(params[:message][:images])
    redirect_to message
  end
end

1. Add require "active_storage" to config/application.rb, after require "rails/all" line.
2. Run rails activestorage:install to create needed directories, migrations, and configuration.
3. Configure the storage service in config/environments/* with config.active_storage.service = :local that references the services configured in config/storage_services.yml.

• Document all the classes
• Strip Download of its responsibilities and delete class
• Convert MirrorService to use threading
• Read metadata via Marcel?
• Add Migrator to copy/move between services
• Explore direct uploads to cloud
• Extract VerifiedKeyWithExpiration into Rails as a feature of MessageVerifier

This separate repository is a staging ground for eventual inclusion in rails/rails prior to the Rails 5.2 release. It is not intended to be a long-term stand-alone repository. Compatibility with prior versions of Rails is not a development priority either.

Active Storage is released under the MIT License.