Administrate::Field::ActiveStorage

• To preview pdf files you need to install mupdf or Poppler.
• To preview video files you need to install ffmpeg.
• To preview Office files as pictures you need to install activestorage-office-previewer by basecamp

Add administrate-field-active_storage and image_processing to your Gemfile (Rails 6+):

gem "administrate-field-active_storage"
gem "image_processing"

for Rails 5.x use the following

gem "administrate-field-active_storage", "0.1.8"

Install:

$ bundle install

Assuming your model name is Model and field name is attachment

class ModelDashboard < Administrate::BaseDashboard
  ATTRIBUTE_TYPES = {
    attachment: Field::ActiveStorage,
  }
# ...

Then add :attachment to FORM_ATTRIBUTES and SHOW_PAGE_ATTRIBUTES. Adding :attachment COLLECTION_ATTRIBUTES will work but will probably look too big.

Assuming your model name is Model and field name is attachments the process is identical the only issue is that the form field isn't being permitted, in order to permit it we apply the following method to the dashboard:

class ModelDashboard < Administrate::BaseDashboard
  ATTRIBUTE_TYPES = {
    attachments: Field::ActiveStorage,
  }

  # ...
  FORM_ATTRIBUTES = {
    #...
    :attachments
  }

  # permitted for has_many_attached
  def permitted_attributes(_action = nil)
    super + [:attachments => []]
  end

I know it is not ideal, if you have a workaround please submit a PR.

Note: Rails 6 introduced a new config to determine the behavior on updates to has_many_attached. Setting Rails.application.config.active_storage.replace_on_assign_to_many to true will overwrite any existing values (purging the old ones), and setting it to false will append the new values. Please note that this configuation was deprecated with Rails 7.1

config.active_storage.replace_on_assign_to_many is deprecated and will be removed in Rails 7.1. Make sure that your code works well with config.active_storage.replace_on_assign_to_many set to true before upgrading. To append new attachables to the Active Storage association, prefer using attach. Using association setter would result in purging the existing attached attachments and replacing them with new ones.

This means that in Rails 7 for has_many_attached, whenever a form is submitted, all associations to existing attachments are being removed without the ActiveStorage objects being deleted. This is undesired behaviour because you have to re attach every time you update an object and it will result in orphaned ActiveStorage objects. To fix this and to add the ability to add more attachments to an existing set of attachments, follow this workaround. In short, you can create a concern:

# app/models/concerns/append_to_has_many_attached.rb
module AppendToHasManyAttached
  def self.[](fields)
    Module.new do
      extend ActiveSupport::Concern

      fields = Array(fields).compact_blank # will always return an array ( worst case is an empty array)

      fields.each do |field|
        field = field.to_s # We need the string version
        define_method :"#{field}=" do |attachables|
          attachables = Array(attachables).compact_blank

          if attachables.any?
            attachment_changes[field] =
              ActiveStorage::Attached::Changes::CreateMany.new(field, self, public_send(field).public_send(:blobs) + attachables)
          end
        end
      end
    end
  end
end

And then load this concern in your model:

class Model < ApplicationModel
  include AppendToHasManyAttached['files'] # you can include it before or after, order does not matter, explanation below

  has_many_attached :files
end

Please note, it does not matter if you prepend or include the module, see original post for details.

In order to prevent N+1 queries from active storage you have to modify your admin model controller, below an example for a model called User and with attached avatars

module Admin
  class UsersController < ApplicationController
    def scoped_resource
      resource_class.with_attached_avatars
    end
  end
end

Administrate::Field::ActiveStorage expects the presence of a route DELETE /<namespace>/<resource>/:id/:attachment_name, which will receive an optional parameter attachment_id in the case of an ActiveStorage::Attached::Many. For instance:

# routes.rb
...
namespace :admin do
  ...
  resources :users do
    delete :avatars, on: :member, action: :destroy_avatar
  end
end

# app/controllers/admin/users_controller.rb
module Admin
  class UsersController < ApplicationController

    # For illustrative purposes only.
    #
    # **SECURITY NOTICE**: first verify whether current user is authorized to perform the action.
    def destroy_avatar
      avatar = requested_resource.avatars.find(params[:attachment_id])
      avatar.purge
      redirect_back(fallback_location: requested_resource)
    end
  end
end

For has_one_attached cases, you will use:

# routes.rb
...
namespace :admin do
  ...
  resources :users do
    delete :avatar, on: :member, action: :destroy_avatar
  end
end

# app/controllers/admin/users_controller.rb
module Admin
  class UsersController < ApplicationController

    # For illustrative purposes only.
    #
    # **SECURITY NOTICE**: first verify whether current user is authorized to perform the action.
    def destroy_avatar
      avatar = requested_resource.avatar
      avatar.purge
      redirect_back(fallback_location: requested_resource)
    end
  end
end

This route can be customized with destroy_url. The option expects a proc receiving 3 arguments: the Administrate namespace, the resource, and the attachment. The proc can return anything accepted by link_to:

# routes.rb
delete :custom_user_avatar_destroy, to: 'users#destroy_avatar'

# user_dashboard.rb
class UserDashboard < Administrate::BaseDashboard
  ATTRIBUTE_TYPES = {
    avatars: Field::ActiveStorage.with_options(
      destroy_url: proc do |namespace, resource, attachment|
        [:custom_user_avatar_destroy, { attachment_id: attachment.id }]
      end
    ),
    # ...
  end
  # ...
end

Various options can be passed to Administrate::Field::ActiveStorage#with_options as illustrated below:

class ModelDashboard < Administrate::BaseDashboard
  ATTRIBUTE_TYPES = {
    attachments: Field::ActiveStorage.with_options(index_display_preview: false),
    # ...
  }
  # ...
end

Display attachment preview.

Defaults to true.

Displays the first attachment (which is the only attachment in case of has_one) in the index action.

Defaults to true.

If true, will show only the preview in the index action, and not the filename or destroy link (if set).

Indicate the size of the image preview for the index and show actions, respectively. Refer to mini_magic#resize_to_limit for documentation.

Default to [150, 150] and [800, 800], respectively.

Use a named variant for image preview for the index and show actions, respectively. Named image variants were added in Rails 7.

It might be necessary to add to app/assets/config/manifest.js:

 //= link 'administrate-field-active_storage/application.css'

When set, this takes precedence over index_preview_size and show_preview_size.

Setting this to false displays original images instead of variants.

Defaults to nil.

Displays the number of attachments in the index action.

Defaults to true if number of attachments is not 1.

Enables direct upload from the browser to the cloud.

Defaults to false.

Don't forget to include ActiveStorage JavaScript. You can use rails generate administrate:assets:javascripts to be able to customize Administrate JavaScripts in your application.

You can see translation example here.

• upload single file
• adding image support through url_for to support 3rd party cloud storage
• use html 5 video element for video files
• use html audio element for audio files
• download link to other files
• preview videos
• preview pdfs
• upload multiple files
• find a way to delete attachments
• preview office files as pictures

1. contributers are welcome (code, suggestions, and bugs).
2. please test your code: cd test_app && bundle && bundle exec rails test.
3. please document your code.
4. add your name to the contribute.md.

Based on the Administrate::Field::Image template, and inspired by Administrate::Field::Paperclip.