Sometimes we have an image url, that we want to “download” and store directly in our app’s storage.

Usecase examples:

  • scrape images from reddit or imgur?
  • User signs up with an oAuth provider, we get an image_url from the oAuth params
  • Import Youtube videos via API and store thumbnail locally from thumbnail_url

Install ActiveStorage:

bin/rails active_storage:install
bin/rails db:migrate
bundle add image_processing

Attach cover_image to Post via ActiveStorage:

# app/models/post.rb
  has_one_attached :cover_image

Job that attaches an image from image_url to a post:

require 'open-uri'

class StoreCoverImageJob < ApplicationJob
  queue_as :default

  PERMIT_IMAGE_FORMAT = %w[png jpg jpeg].freeze

  def perform(post, image_url)
    valid_image_format = get_content_type(image_url)
    return unless valid_image_format

    uri = URI.parse(image_url)
    image =
    image_name = File.basename(image_url)
    post.cover_image.attach(io: image, filename: image_name, content_type: valid_image_format)


  def get_content_type(image_url)
    ext_name = File.extname(image_url).delete('.')
    return unless PERMIT_IMAGE_FORMAT.include?(ext_name)


Try it in your rails console:

post = Post.first
post.cover_image.attached? #=> false
image_url = ""
StoreCoverImageJob.perform_now(post, image_url)
post.cover_image.attached? #=> true

Testing #

Test StoreCoverImageJob:

# test/jobs/youtube/store_cover_image_job_test.rb
require 'test_helper'

class StoreCoverImageJobTest < ActiveJob::TestCase
  test 'attach cover image' do
    post = posts(:one)
    assert_not post.cover_image.attached?


    assert post.reload.cover_image.attached?

Test has_one_attached :cover_image

# test/models/post_cover_image_test.rb
require 'test_helper'

class PostTest < ActiveSupport::TestCase
  test 'cover_image is attached to post' do
    post =
    post.cover_image.attach(io: Rails.root.join('test/fixtures/files/image.jpg').open,
                            filename: 'image.jpg',
                            content_type: 'image/jpeg')

    assert post.valid?
    assert post.cover_image.attached?
    assert_equal 'image.jpg', post.cover_image.filename.to_s
    assert_equal 'image/jpeg', post.cover_image.content_type

That’s it!