Example migration for changing paperclip storage path

20160307172445_change_paperclip_attachment_path.rb

class MoveAttachmentsToNewLocation < ActiveRecord::Migration
  def initialize(name = self.class.name, version = nil)
    access_key = Rails.application.secrets.g3_access_key_id
    secret_key = Rails.application.secrets.g3_secret_access_key
    storage = Fog::Storage::Google.new google_storage_access_key_id: access_key,
                                       google_storage_secret_access_key: secret_key

    @bucket_name = Rails.application.secrets.g3_bucket
    @bucket = storage.directories.get(@bucket_name)
    super(name, version)
  end

  def copy_helper(attachment, style)
    old_path = Paperclip::Interpolations.interpolate(@original_path_string, attachment, style)
    new_path = Paperclip::Interpolations.interpolate(@new_path_string, attachment, style)

    file = @bucket.files.get(old_path)
    return unless !file.nil?

    copy = file.copy(@bucket_name, new_path)
    copy.public = true
    copy.save
    file.destroy
  end

  def up
    @original_path_string = ":class/:attachment/:id_partition/:style/:filename"
    @new_path_string = "my/new/path/:filename.:extension"

    # model_with_attachemnt
    items = ModelWithAttachment.all
    items.each do |item|
      styles = [:medium]
      styles.each do |style|
        attachments = [item.avatar]
        attachments.each do |attachment|
          copy_helper(attachment, style)
        end
      end
    end

    # other_model_with_attachments
    items = OtherModelWithAttachments.all
    items.each do |item|
      styles = [:medium, :thumb]
      styles.each do |style|
        attachments = [item.avatar, item.image]
        attachments.each do |attachment|
          copy_helper(attachment, style)
        end
      end
    end
  end

  def down
    @original_path_string = "my/new/path/:filename.:extension"
    @new_path_string = ":class/:attachment/:id_partition/:style/:filename"

    # model_with_attachemnt
    items = ModelWithAttachment.all
    items.each do |item|
      styles = [:medium]
      styles.each do |style|
        attachments = [item.avatar]
        attachments.each do |attachment|
          copy_helper(attachment, style)
        end
      end
    end

    # other_model_with_attachments
    items = OtherModelWithAttachments.all
    items.each do |item|
      styles = [:medium, :thumb]
      styles.each do |style|
        attachments = [item.avatar, item.image]
        attachments.each do |attachment|
          copy_helper(attachment, style)
        end
      end
    end
  end
end

return unless !file.nil? -> return if file.nil?