rails--rails/activestorage/README.md

Active Storage

Active Storage makes it simple to upload and reference files in cloud services, like Amazon S3, Google Cloud Storage or Microsoft Azure 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.

Files can uploaded from the server to the cloud or directly from the client to the cloud.

Image files can further more be transformed using on-demand variants for quality, aspect ratio, size, or any other MiniMagick supported transformation.

Compared to other storage solutions

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 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).

Examples

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.attached? # => true

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

url_for(user.avatar) # Generate a permanent URL for the blob, which upon access will redirect to a temporary service URL.

class AvatarsController < ApplicationController
  def update
    # params[:avatar] contains a ActionDispatch::Http::UploadedFile object
    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 index
    # Use the built-in with_attached_images scope to avoid N+1
    @messages = Message.all.with_attached_images
  end

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

  def show
    @message = Message.find(params[:id])
  end
end

Variation of image attachment:

<%# Hitting the variant URL will lazy transform the original blob and then redirect to its new service location %>
<%= image_tag url_for(user.avatar.variant(resize: "100x100")) %>

Installation

1. Run rails activestorage:install to create needed directories, migrations, and configuration.
2. Optional: Add gem "aws-sdk", "~> 2" to your Gemfile if you want to use AWS S3.
3. Optional: Add gem "google-cloud-storage", "~> 1.3" to your Gemfile if you want to use Google Cloud Storage.
4. Optional: Add gem "azure-storage" to your Gemfile if you want to use Microsoft Azure.
5. Optional: Add gem "mini_magick" to your Gemfile if you want to use variants.

Direct uploads

Active Storage, with its included JavaScript library, supports uploading directly from the client to the cloud.

Direct upload installation

1. Include activestorage.js in your application's JavaScript bundle.

   Using the asset pipeline:

   //= require activestorage
   

   Using the npm package:

   import * as ActiveStorage from "activestorage"
   ActiveStorage.start()
   

2. Annotate file inputs with the direct upload URL.

   <%= form.file_field :attachments, multiple: true, direct_upload: true %>
   

3. That's it! Uploads begin upon form submission.

Direct upload JavaScript events

Event name	Event target	Event data (event.detail)	Description
direct-uploads:start	<form>	None	A form containing files for direct upload fields was submit.
direct-upload:initialize	<input>	{id, file}	Dispatched for every file after form submission.
direct-upload:start	<input>	{id, file}	A direct upload is starting.
direct-upload:before-blob-request	<input>	{id, file, xhr}	Before making a request to your application for direct upload metadata.
direct-upload:before-storage-request	<input>	{id, file, xhr}	Before making a request to store a file.
direct-upload:progress	<input>	{id, file, progress}	As requests to store files progress.
direct-upload:error	<input>	{id, file, error}	An error occurred. An alert will display unless this event is canceled.
direct-upload:end	<input>	{id, file}	A direct upload has ended.
direct-uploads:end	<form>	None	All direct uploads have ended.

License

Active Storage is released under the MIT License.