Ruby Rails，具有带有自定义模型属性的附加文件路径

我想用一些模型的属性自定义has_attached_文件路径

这是带有附加文件的模型：

class Picture < ActiveRecord::Base

  belongs_to :with_content, :polymorphic => true

  has_attached_file :picture, {
    :styles => { :mobile => ["320x200#", :png], :original => ["1280x1024>", :jpg] },
    :path => ":rails_root/public/:class/:with_content_type/:style_:basename.:extension"
  }
}

 Paperclip.interpolates :with_content_type do |attachment, style|
    "#{attachment.instance.with_content_type}"
  end