**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON https://guides.rubyonrails.org.**
Active Storage Overview
=======================
This guide covers how to attach files to your Active Record models.
After reading this guide, you will know:
* How to attach one or many files to a record.
* How to delete an attached file.
* How to link to an attached file.
* How to use variants to transform images.
* How to generate an image representation of a non-image file, such as a PDF or a video.
* How to send file uploads directly from browsers to a storage service,
bypassing your application servers.
* How to clean up files stored during testing.
* How to implement support for additional storage services.
--------------------------------------------------------------------------------
What is Active Storage?
-----------------------
Active Storage facilitates uploading files to a cloud storage service like
Amazon S3, Google Cloud Storage, or Microsoft Azure Storage and attaching those
files to Active Record objects. It comes with a local disk-based service for
development and testing and supports mirroring files to subordinate services for
backups and migrations.
Using Active Storage, an application can transform image uploads with
[ImageMagick](https://www.imagemagick.org), generate image representations of
non-image uploads like PDFs and videos, and extract metadata from arbitrary
files.
## Setup
Active Storage uses two tables in your application’s database named
`active_storage_blobs` and `active_storage_attachments`. After creating a new
application (or upgrading your application to Rails 5.2), run
`rails active_storage:install` to generate a migration that creates these
tables. Use `rails db:migrate` to run the migration.
WARNING: `active_storage_attachments` is a polymorphic join table that stores your model's class name. If your model's class name changes, you will need to run a migration on this table to update the underlying `record_type` to your model's new class name.
Declare Active Storage services in `config/storage.yml`. For each service your
application uses, provide a name and the requisite configuration. The example
below declares three services named `local`, `test`, and `amazon`:
```yaml
local:
service: Disk
root: <%= Rails.root.join("storage") %>
test:
service: Disk
root: <%= Rails.root.join("tmp/storage") %>
amazon:
service: S3
access_key_id: ""
secret_access_key: ""
bucket: ""
region: "" # e.g. 'us-east-1'
```
Tell Active Storage which service to use by setting
`Rails.application.config.active_storage.service`. Because each environment will
likely use a different service, it is recommended to do this on a
per-environment basis. To use the disk service from the previous example in the
development environment, you would add the following to
`config/environments/development.rb`:
```ruby
# Store files locally.
config.active_storage.service = :local
```
To use the Amazon S3 service in production, you add the following to
`config/environments/production.rb`:
```ruby
# Store files on Amazon S3.
config.active_storage.service = :amazon
```
To use the test service when testing, you add the following to
`config/environments/test.rb`:
```ruby
# Store uploaded files on the local file system in a temporary directory.
config.active_storage.service = :test
```
Continue reading for more information on the built-in service adapters (e.g.
`Disk` and `S3`) and the configuration they require.
### Disk Service
Declare a Disk service in `config/storage.yml`:
```yaml
local:
service: Disk
root: <%= Rails.root.join("storage") %>
```
### Amazon S3 Service
Declare an S3 service in `config/storage.yml`:
```yaml
amazon:
service: S3
access_key_id: ""
secret_access_key: ""
region: ""
bucket: ""
```
Add the [`aws-sdk-s3`](https://github.com/aws/aws-sdk-ruby) gem to your `Gemfile`:
```ruby
gem "aws-sdk-s3", require: false
```
NOTE: The core features of Active Storage require the following permissions: `s3:ListBucket`, `s3:PutObject`, `s3:GetObject`, and `s3:DeleteObject`. If you have additional upload options configured such as setting ACLs then additional permissions may be required.
NOTE: If you want to use environment variables, standard SDK configuration files, profiles,
IAM instance profiles or task roles, you can omit the `access_key_id`, `secret_access_key`,
and `region` keys in the example above. The Amazon S3 Service supports all of the
authentication options described in the [AWS SDK documentation]
(https://docs.aws.amazon.com/sdk-for-ruby/v3/developer-guide/setup-config.html).
### Microsoft Azure Storage Service
Declare an Azure Storage service in `config/storage.yml`:
```yaml
azure:
service: AzureStorage
storage_account_name: ""
storage_access_key: ""
container: ""
```
Add the [`azure-storage`](https://github.com/Azure/azure-storage-ruby) gem to your `Gemfile`:
```ruby
gem "azure-storage", require: false
```
### Google Cloud Storage Service
Declare a Google Cloud Storage service in `config/storage.yml`:
```yaml
google:
service: GCS
credentials: <%= Rails.root.join("path/to/keyfile.json") %>
project: ""
bucket: ""
```
Optionally provide a Hash of credentials instead of a keyfile path:
```yaml
google:
service: GCS
credentials:
type: "service_account"
project_id: ""
private_key_id: <%= Rails.application.credentials.dig(:gcs, :private_key_id) %>
private_key: <%= Rails.application.credentials.dig(:gcs, :private_key).dump %>
client_email: ""
client_id: ""
auth_uri: "https://accounts.google.com/o/oauth2/auth"
token_uri: "https://accounts.google.com/o/oauth2/token"
auth_provider_x509_cert_url: "https://www.googleapis.com/oauth2/v1/certs"
client_x509_cert_url: ""
project: ""
bucket: ""
```
Add the [`google-cloud-storage`](https://github.com/GoogleCloudPlatform/google-cloud-ruby/tree/master/google-cloud-storage) gem to your `Gemfile`:
```ruby
gem "google-cloud-storage", "~> 1.11", require: false
```
### Mirror Service
You can keep multiple services in sync by defining a mirror service. A mirror
service replicates uploads and deletes across two or more subordinate services.
A mirror service is intended to be used temporarily during a migration between
services in production. You can start mirroring to a new service, copy
pre-existing files from the old service to the new, then go all-in on the new
service.
NOTE: Mirroring is not atomic. It is possible for an upload to succeed on the
primary service and fail on any of the subordinate services. Before going
all-in on a new service, verify that all files have been copied.
Define each of the services you'd like to mirror as described above. Reference
them by name when defining a mirror service:
```yaml
s3_west_coast:
service: S3
access_key_id: ""
secret_access_key: ""
region: ""
bucket: ""
s3_east_coast:
service: S3
access_key_id: ""
secret_access_key: ""
region: ""
bucket: ""
production:
service: Mirror
primary: s3_east_coast
mirrors:
- s3_west_coast
```
Although all secondary services receive uploads, downloads are always handled
by the primary service.
Mirror services are compatible with direct uploads. New files are directly
uploaded to the primary service. When a directly-uploaded file is attached to a
record, a background job is enqueued to copy it to the secondary services.
Attaching Files to Records
--------------------------
### `has_one_attached`
The `has_one_attached` macro sets up a one-to-one mapping between records and
files. Each record can have one file attached to it.
For example, suppose your application has a `User` model. If you want each user to
have an avatar, define the `User` model like this:
```ruby
class User < ApplicationRecord
has_one_attached :avatar
end
```
You can create a user with an avatar:
```erb
<%= form.file_field :avatar %>
```
```ruby
class SignupController < ApplicationController
def create
user = User.create!(user_params)
session[:user_id] = user.id
redirect_to root_path
end
private
def user_params
params.require(:user).permit(:email_address, :password, :avatar)
end
end
```
Call `avatar.attach` to attach an avatar to an existing user:
```ruby
user.avatar.attach(params[:avatar])
```
Call `avatar.attached?` to determine whether a particular user has an avatar:
```ruby
user.avatar.attached?
```
### `has_many_attached`
The `has_many_attached` macro sets up a one-to-many relationship between records
and files. Each record can have many files attached to it.
For example, suppose your application has a `Message` model. If you want each
message to have many images, define the `Message` model like this:
```ruby
class Message < ApplicationRecord
has_many_attached :images
end
```
You can create a message with images:
```ruby
class MessagesController < ApplicationController
def create
message = Message.create!(message_params)
redirect_to message
end
private
def message_params
params.require(:message).permit(:title, :content, images: [])
end
end
```
Call `images.attach` to add new images to an existing message:
```ruby
@message.images.attach(params[:images])
```
Call `images.attached?` to determine whether a particular message has any images:
```ruby
@message.images.attached?
```
### Attaching File/IO Objects
Sometimes you need to attach a file that doesn’t arrive via an HTTP request.
For example, you may want to attach a file you generated on disk or downloaded
from a user-submitted URL. You may also want to attach a fixture file in a
model test. To do that, provide a Hash containing at least an open IO object
and a filename:
```ruby
@message.image.attach(io: File.open('/path/to/file'), filename: 'file.pdf')
```
When possible, provide a content type as well. Active Storage attempts to
determine a file’s content type from its data. It falls back to the content
type you provide if it can’t do that.
```ruby
@message.image.attach(io: File.open('/path/to/file'), filename: 'file.pdf', content_type: 'application/pdf')
```
You can bypass the content type inference from the data by passing in
`identify: false` along with the `content_type`.
```ruby
@message.image.attach(
io: File.open('/path/to/file'),
filename: 'file.pdf',
content_type: 'application/pdf',
identify: false
)
```
If you don’t provide a content type and Active Storage can’t determine the
file’s content type automatically, it defaults to application/octet-stream.
Removing Files
--------------
To remove an attachment from a model, call `purge` on the attachment. Removal
can be done in the background if your application is setup to use Active Job.
Purging deletes the blob and the file from the storage service.
```ruby
# Synchronously destroy the avatar and actual resource files.
user.avatar.purge
# Destroy the associated models and actual resource files async, via Active Job.
user.avatar.purge_later
```
Linking to Files
----------------
Generate a permanent URL for the blob that points to the application. Upon
access, a redirect to the actual service endpoint is returned. This indirection
decouples the public URL from the actual one, and allows, for example, mirroring
attachments in different services for high-availability. The redirection has an
HTTP expiration of 5 min.
```ruby
url_for(user.avatar)
```
To create a download link, use the `rails_blob_{path|url}` helper. Using this
helper allows you to set the disposition.
```ruby
rails_blob_path(user.avatar, disposition: "attachment")
```
If you need to create a link from outside of controller/view context (Background
jobs, Cronjobs, etc.), you can access the rails_blob_path like this:
```
Rails.application.routes.url_helpers.rails_blob_path(user.avatar, only_path: true)
```
Downloading Files
-----------------
Sometimes you need to process a blob after it’s uploaded—for example, to convert
it to a different format. Use `ActiveStorage::Blob#download` to read a blob’s
binary data into memory:
```ruby
binary = user.avatar.download
```
You might want to download a blob to a file on disk so an external program (e.g.
a virus scanner or media transcoder) can operate on it. Use
`ActiveStorage::Blob#open` to download a blob to a tempfile on disk:
```ruby
message.video.open do |file|
system '/path/to/virus/scanner', file.path
# ...
end
```
Transforming Images
-------------------
To create a variation of the image, call `variant` on the `Blob`. You can pass
any transformation to the method supported by the processor. The default
processor is [MiniMagick](https://github.com/minimagick/minimagick), but you
can also use [Vips](https://www.rubydoc.info/gems/ruby-vips/Vips/Image).
To enable variants, add the `image_processing` gem to your `Gemfile`:
```ruby
gem 'image_processing', '~> 1.2'
```
When the browser hits the variant URL, Active Storage will lazily transform the
original blob into the specified format and redirect to its new service
location.
```erb
<%= image_tag user.avatar.variant(resize_to_limit: [100, 100]) %>
```
To switch to the Vips processor, you would add the following to
`config/application.rb`:
```ruby
# Use Vips for processing variants.
config.active_storage.variant_processor = :vips
```
Previewing Files
----------------
Some non-image files can be previewed: that is, they can be presented as images.
For example, a video file can be previewed by extracting its first frame. Out of
the box, Active Storage supports previewing videos and PDF documents.
```erb
<% @message.files.each do |file| %>
-
<%= image_tag file.preview(resize_to_limit: [100, 100]) %>
<% end %>
```
WARNING: Extracting previews requires third-party applications, FFmpeg for
video and muPDF for PDFs, and on macOS also XQuartz and Poppler.
These libraries are not provided by Rails. You must install them yourself to
use the built-in previewers. Before you install and use third-party software,
make sure you understand the licensing implications of doing so.
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:
```js
//= require activestorage
```
Using the npm package:
```js
require("@rails/activestorage").start()
```
2. Annotate file inputs with the direct upload URL.
```erb
<%= 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` | `