Migrate file uploads from database to Amazon S3 in Rails

migrate_file_uploads_from_database_to_amazon_in_rails.rake

task migrate_file_uploads_from_database_to_amazon: :environment do
  Document.find_each do |d| # Document is our ActiveRecord model containing the `data` binary column (bytea Postgres type)
    next if ENV['ID'] && d.id.to_s != ENV['ID'] # be able to say `ID=225 rake migrate_file_uploads_from_database_to_amazon` to process single record
    next unless d.data # d.data is a binary column we were storing files at
    print d.id

    dir = "tmp/#{d.id}"

    Dir.mkdir(dir) unless Dir.exist?(dir)

    name = d.read_attribute(:name)
    path = "#{dir}/#{name}"
    File.open(path, "w+b") do |f|
      f.write d.data
    end

    File.open(path) do |f|
      d.document_file = f # new column mounted with Carrierwave generated DocumentUploader
      d.save!
    end

    print '.'
  end
end