anex = Anex.new(file_data_uri: file) # file is a base64 string
resource.anexes << anex
resource.save!

require "shrine"
require "shrine/storage/file_system"

Shrine.storages = {
  cache: Shrine::Storage::FileSystem.new("public", prefix: "uploads/cache"), # temporary
  store: Shrine::Storage::FileSystem.new("public", prefix: "uploads/store"), # permanent
}

Shrine.plugin :activerecord
Shrine.plugin :cached_attachment_data # for forms
Shrine.plugin :data_uri # for base_64
Shrine.plugin :infer_extension
# Shrine.plugin :rack_file # for non-Rails apps

class FileUploader < Shrine
  # plugins and uploading logic

end

class Anex < ApplicationRecord
  belongs_to :anexable, polymorphic: true

  include FileUploader::Attachment.new(:file) # adds an `file` virtual attribute

  def url
    "#{ENV['FILE_STORAGE_URI']}#{self.file.url}"
  end
end