ActiveStorage 从 S3 服务上的附件对象下载文件/IO？

Question

After the file is uploaded, I want to analyze and immediately process.

I'm currently attaching then processing each:

current_account.archives.attach(archive_params)
current_account.archives.each do |archive|
  Job.enqueue(AccountArchiveImportJob.new(current_account.id, archive.id))
end

In the job i'm opening the CSV and parsing junk

attachment = Account.find(account_id).archives.where(id: archive_id).first

CSV.parse(attachment.download) do |row|
  do_stuff_with_the_row(row)
end

I would like to do something like:

CSV.foreach(attachment.open) do |row|
  do_stuff_with_the_row(row)
end

I cannot find documentation that allows converting the attachment back into a FILE

Answer 1

At least from Rails 6.0 rc1:

model.attachment_changes['attachment_name'].attachable

will give you IO of the original TmpFile BEFORE it is uploaded.

Answer 2

Rails-6 we will get a download method that will yield a file but you can get this very easily!

Add this downloader.rb file as an initializer

Then given this model

class Business < ApplicationRecord
  has_one_attached :csvfile
end

you can do

ActiveStorage::Downloader.new(csvfile).download_blob_to_tempfile do |file|
  CSV.foreach(file.path, {headers: true}) do |row|
    do_something_with_each_row(row.to_h)
  end
end

EDIT : not sure why this took me to so long to find service_url . Way more simple, but has been noted that service_url should not be shown to users

open(csvfile.service_url)

Answer 3

You can get the file path from the attachment, and then open the file.

path = ActiveStorage::Blob.service.send(:path_for, attachment.key)
File.open(path) do |file|
    #...
end

Answer 4

From Rails 5.2 official guide

class VirusScanner
  include ActiveStorage::Downloading

  attr_reader :blob

  def initialize(blob)
    @blob = blob
  end

  def scan
    download_blob_to_tempfile do |file|
      system 'scan_virus', file.path
    end
  end
end

So you can do

  include ActiveStorage::Downloading

  attr_reader :blob

  def initialize(blob)
    @blob = blob
  end

  def perform
    download_blob_to_tempfile do |file|
      CSV.foreach(file.path, {headers: true}) do |row|
        do_something_with_each_row(row.to_h)
      end
    end
  end