Minimal active storage example

config.ru

# 1. Put this file into the root of rails repo
# 2. `bundle exec rackup -b 0.0.0.0`
# 3. `open localhost:9292`
require 'rails/all'

tmpdir = Dir.mktmpdir
Dir.chdir(tmpdir)

ENV['DATABASE_URL'] = "sqlite3://#{File.join(tmpdir, 'database.sql')}"

class TestApp < Rails::Application
  secrets.secret_key_base = 'secret_key_base'
end

Rails.application.configure do
  config.load_defaults 5.2
  config.eager_load = true
  config.active_storage.service = :local
  config.logger = ActiveSupport::Logger.new(STDOUT)
  config.active_storage.service_configurations = {
    local: {
      service: 'Disk',
      root: tmpdir
    }
  }

  config.after_initialize do |app|
    ActiveRecord::Schema.define do
      create_table :users, force: true do |t|
      end

      load File.join(Bundler.rubygems.find_name('activestorage').first.full_gem_path, 'db/migrate/20170806125915_create_active_storage_tables.rb')

      CreateActiveStorageTables.new.change
    end

    class User < ActiveRecord::Base
      has_one_attached :avatar
    end

    class UsersController < ActionController::Base
      def index
        @user = User.new

        render inline: <<~ERB
          <%= form_with model: @user do |f| %>
            <%= f.file_field :avatar %>
            <%= f.submit %>
          <% end %>

          <ul>
            <%- User.all.each do |u| %>
              <li>
                <div>id: <%= u.id %></div>
                <%= link_to 'download via send_data', user_path(u.id) %>
                <%= link_to 'download via rails_blob_path', rails_blob_path(u.avatar, disposition: 'attachment') %>
              </li>
            <% end %>
          </ul>
        ERB
      end

      def create
        User.create!(params.require(:user).permit(:avatar))

        redirect_to users_path
      end

      def show
        user = User.find(params[:id])

        send_data user.avatar.download, disposition: 'attachment', filename: user.avatar.filename.to_s
      end
    end

    app.routes.prepend do
      root to: redirect('/users')
      resources :users
    end

    user = User.new
    user.avatar.attach(io: File.open(__FILE__), filename: %(あ"い"\\う/え'お.rb))
    user.save!
  end
end
Rails.application.initialize!
run Rails.application

at_exit do
  FileUtils.rm_rf(tmpdir)
end