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# Active Storage
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.
## 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](https://github.com/rails/activestorage/blob/master/lib/active_storage/blob.rb) and [Attachment](https://github.com/rails/activestorage/blob/master/lib/active_storage/attachment.rb) 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).
## Examples
One attachment:
```ruby
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:
```ruby
class Message < ApplicationRecord
has_many_attached :images
end
```
```erb
<%= 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 %>
```
```ruby
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
```
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 url_for(user.avatar.variant(resize: "100x100")) %>
```
## Installation
1. Add `gem "activestorage", git: "https://github.com/rails/activestorage.git"` to your Gemfile.
2. Add `require "active_storage"` to config/application.rb, after `require "rails/all"` line.
3. Run `rails activestorage:install` to create needed directories, migrations, and configuration.
4. Configure the storage service in `config/environments/*` with `config.active_storage.service = :local`
that references the services configured in `config/storage_services.yml`.
5. Optional: Add `gem "mini_magick"` to your Gemfile if you want to use variants.
## Todos
- 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](https://github.com/rails/activestorage/pull/19)
- Extract VerifiedKeyWithExpiration into Rails as a feature of MessageVerifier
## Roadmap
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.
## License
Active Storage is released under the [MIT License](https://opensource.org/licenses/MIT).
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