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 be 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](https://github.com/rails/rails/blob/master/activestorage/app/models/active_storage/blob.rb) and [Attachment](https://github.com/rails/rails/blob/master/activestorage/app/models/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 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.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:

```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 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:

```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: "100x100") %>
```

## 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
    import * as ActiveStorage from "activestorage"
    ActiveStorage.start()
    ```
2. Annotate file inputs with the direct upload URL.

    ```ruby
    <%= 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 submitted. |
| `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](https://opensource.org/licenses/MIT).