Attach cloud and local files in Rails applications
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. Supports having one main service and mirrors in other services for redundancy. It also provides a disk service for testing or local deployments, but the focus is on cloud storage.
Files can be uploaded from the server to the cloud or directly from the client to the cloud.
Image files can furthermore be transformed using on-demand variants for quality, aspect ratio, size, or any other MiniMagick or Vips supported transformation.
You can read more about Active Storage in the Active Storage Overview guide.
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 Attachment join model, which then connects to the actual Blob.
Blob models store attachment metadata (filename, content-type, etc.), and their identifier key in the storage service. Blob models do not store the actual binary data. They 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 one (though of course you can delete the previous version later if you don't need it).
Run bin/rails active_storage:install to copy over active_storage migrations.
NOTE: If the task cannot be found, verify that require "active_storage/engine" is present in config/application.rb.
One attachment:
``ruby
class User < ApplicationRecord
# Associates an attachment and a blob. When the user is destroyed they are
# purged by default (models destroyed, and resource files deleted).
has_one_attached :avatar
end
class AvatarsController < ApplicationController
def update
# params[:avatar] contains an ActionDispatch::Http::UploadedFile object
Current.user.avatar.attach(params.require(:avatar))
redirect_to Current.user
end
end
`
Many attachments:
`ruby`
class Message < ApplicationRecord
has_many_attached :images
end
`erb
<%= form_with model: @message, local: true do |form| %>
<%= form.text_field :title, placeholder: "Title" %>
<%= form.textarea :content %>
<%= form.file_field :images, multiple: true %>
<%= form.submit %>
<% end %>
`
`ruby
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.expect(message: [ :title, :content, images: [] ])
redirect_to message
end
def show
@message = Message.find(params[:id])
end
end
`
Variation of image attachment:
`erb`
<%# Hitting the variant URL will lazy transform the original blob and then redirect to its new service location %>
<%= image_tag user.avatar.variant(resize_to_limit: [100, 100]) %>
Active Storage supports two ways to serve files: redirecting and proxying.
Active Storage generates stable application URLs for files which, when accessed, redirect to signed, short-lived service URLs. This relieves application servers of the burden of serving file data. It is the default file serving strategy.
When the application is configured to proxy files by default, use the rails_storage_redirect_path and _url route helpers to redirect instead:
`erb`
<%= image_tag rails_storage_redirect_path(@user.avatar) %>
Optionally, files can be proxied instead. This means that your application servers will download file data from the storage service in response to requests. This can be useful for serving files from a CDN.
You can configure Active Storage to use proxying by default:
`ruby`config/initializers/active_storage.rb
Rails.application.config.active_storage.resolve_model_to_route = :rails_storage_proxy
Or if you want to explicitly proxy specific attachments there are URL helpers you can use in the form of rails_storage_proxy_path and rails_storage_proxy_url.
`erb`
<%= image_tag rails_storage_proxy_path(@user.avatar) %>
Active Storage, with its included JavaScript library, supports uploading directly from the client to the cloud.
1. Include the Active Storage JavaScript in your application's JavaScript bundle or reference it directly.
Requiring directly without bundling through the asset pipeline in the application HTML with autostart:
`erb`
<%= javascript_include_tag "activestorage" %>
Requiring via importmap-rails without bundling through the asset pipeline in the application HTML without autostart as ESM:
ruby`
# config/importmap.rb
pin "@rails/activestorage", to: "activestorage.esm.js"
html`
Using the asset pipeline:
js`
//= require activestorage
Using the npm package:
js`
import * as ActiveStorage from "@rails/activestorage"
ActiveStorage.start()
2. Annotate file inputs with the direct upload URL.
`erb`
<%= form.file_field :attachments, multiple: true, direct_upload: true %>
3. Configure CORS on third-party storage services to allow direct upload requests.
4. That's it! Uploads begin upon form submission.
| Event name | Event target | Event data (event.detail) | Description |direct-uploads:start
| --- | --- | --- | --- |
| |