使用Paperclip gem动态生成Amazon S3资产的文件路径

Question

I'm successfully using the Paperclip gem to upload files to Amazon S3. My question is, how can I configure my model to change the file path based on object attributes?

For example, I want an image of a 2015 RAM 1500 to be uploaded to "cars/2015/RAM/1500/:id."

Here's what I tried. The ":id/:style_:extension" gets replaced with the correct information, but the other attributes do not - even though each car has a year, manufacturer, and model.

class Car < ActiveRecord::Base
  has_attached_file :file, default_url: "/images/:style/missing.png"
  validates_attachment_content_type :file, content_type: /\Aimage\/.*\Z/
  has_attached_file :file,
                :storage => :s3,
                :path => "cars/:year/:manufacturer/:model/:id/:style_:extension",
                :s3_credentials => Proc.new{|a| a.instance.s3_credentials }

  belongs_to :manufacturer

  def s3_credentials
    {:bucket => ENV['bucket'], :access_key_id => ENV['access_key_id'], :secret_access_key => ENV['secret_access_key']}
  end
end

Answer 1

Ok, it's in the docs (oops): Paperclip Interpolations

I added this block for each attribute I needed to interpolate to my car model:

Paperclip.interpolates :year do |attachment, style|
  attachment.instance.year
end

Answer 2

Here's another way you could do it, which is pretty clean and reusable. While Concerns are sometimes frowned upon, this is one of the cases when they are very useful!

# lib/interpolates.rb
module Interpolates
  extend ActiveSupport::Concern

  included do
      def self.interpolates(attr)
          Paperclip.interpolates(attr) do |attachment, style|
              attachment.instance.send(attr)
          end
      end
  end
end

And then, in any of your models:

# models/car.rb
class Car < ApplicationRecord
  include Interpolates

  interpolates :manufacturer

  # ...
end

And then, you can use that in any model you want, with very little code!