paperclip_migration.rake

# First configure your models to use Amazon s3 as storage option and setup the associated S3 config.
# Then add the classes your want to migrate in the klasses array below.
# Then run rake paperclip_migration:migrate_to_s3
# Should work but this is untested and may need some tweaking - but it did the job for me.

namespace :paperclip do
  desc "migrate files from local filesystem to s3"
  task :migrate_to_s3 => :environment do

    Rails.application.eager_load!
    ActiveRecord::Base.descendants.select do |d|
      # fix PgSearch and any other gem that creates a model without a valid table
      ActiveRecord::Base.connection.tables.include? d.table_name
    end.each do |klass|

      definitions = klass.try(:attachment_definitions) || {}
      puts(definitions.blank? ? "Skipping #{klass.name} (no attachments)" : "Processing #{klass.name}")

      klass.find_each do |record|
        definitions.keys.each do |definition|

          if !record.send("#{definition}_file_name")
            puts "#{klass.name} #{record.id} has no attachment"
            next
          end

          attachment = Paperclip::Attachment.new(definition.to_sym, record, definitions[definition.to_sym].except(:s3_credentials, :storage))
          attachment_url = attachment.url(attachment.default_style, false)
          attachment_path = (attachment.path[0] == '/' ? '' : Rails.root.to_s + "/public/system") + attachment.path

          if !File.exists?(attachment_path)
            puts "#{klass.name} #{record.id} has a dangling file path or is stored remotely"
            next
          end

          File.open attachment_path do |file|
            puts "#{attachment_path} => S3... "
            record.update_attribute "#{definition}", file
          end
        end
      end
      puts ''
    end
  end
end