README.md

Upload a file in Rails, parse it, then throw it away

You don't need Paperclip or Carrierwave or even an ActiveRecord model to manage file uploads in Rails if all you need to do is read the file in and extract data from it.

The Catalog class (referenced in the UploadController#create method) knows how to read a JSON file, translate and extract the data therein, and create or modify Book and Product records in the surrounding application.

By using the FileUtils.cp class method, we move the uploaded file into a known location at a known filename, so the Catalog (PORO) can do its work. The tempfile created by Rack during the upload is harvested as normal by garbage collection, but the copy we made is deleted manually after the parsing process is completed.

new.html.erb

<!-- in /views/upload -->
<%= form_tag 'create', multipart: true do %>
<div class="field form-group">
  <%= label_tag 'upload[file]', 'Upload catalog.json file' %><br>
  <%= file_field_tag 'upload[file]' %>
</div>
<div class="actions form-group">
  <%= submit_tag 'Upload', class: 'btn btn-primary', data: { disable_with: 'Uploading' } %>
</div>
<%- end -%>

routes.rb

#...
  get 'upload/new'
  post 'upload/create'
# ...

upload_controller.rb

class UploadController < ApplicationController
  before_filter :authenticate_admin!
  authorize_resource :class => false
  require 'fileutils'

  def new
    
  end

  def create
    tmp = params[:upload][:file].tempfile
    file = File.join("tmp", params[:upload][:file].original_filename)
    if file
      FileUtils.cp tmp.path, file
      Catalog.new(file)
      FileUtils.rm file
      redirect_to books_path
    else
      render action: 'new'
    end
  end
end