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Adding Direct App Uploads

Hiren Mistry edited this page Mar 10, 2020 · 27 revisions

This walkthrough shows how to add asynchronous uploads to a Rails app. The flow will go like this:

  1. User selects file(s)
  2. Files are uploaded asynchronously to an upload endpoint on your app
  3. Uploaded file JSON data is written to a hidden field
  4. Form is submitted instantaneously as it only has to submit the JSON data
  5. JSON data is assigned to the Shrine attachment attribute

1. Installation

Add Shrine to the Gemfile:

# Gemfile
# ...
gem "shrine", "~> 3.0"

and run bundle install.

2. Initializer

Create an initializer which configures your storage and loads default plugins:

# config/initializers/shrine.rb

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

Shrine.storages = {
  cache:"public", prefix: "uploads/cache"),
  store:"public", prefix: "uploads"),

Shrine.plugin :activerecord           # load Active Record integration
Shrine.plugin :cached_attachment_data # for retaining cached file on form redisplays
Shrine.plugin :restore_cached_data    # refresh metadata for cached files

3. Migration

Add the <attachment>_data text or JSON column to the table to which you want to add the attachment:

$ rails generate migration add_image_data_to_photos image_data:text # or :jsonb

This should generate the following migration:

class AddImageDataToPhotos < ActiveRecord::Migration
  def change
    add_column :photos, :image_data, :text # or :jsonb

Run rails db:migrate to apply the migration.

4. Attachment

Create an uploader for the types of files you'll be uploading:

# app/uploaders/image_uploader.rb

class ImageUploader < Shrine

and add an attachment attribute to your model:

# app/models/photo.rb

class Photo < ApplicationRecord
  include ImageUploader::Attachment(:image)

  validates_presence_of :image

5. Form

In your form you can now add form fields for the attachment attribute, and an image tag for the preview:

<!-- app/views/photos/_form.html.erb -->

<%= form_for @photo do |f| %>
  <!-- ... -->
    <%= f.label :image %>
    <%= f.hidden_field :image, value: @photo.cached_image_data, class: "upload-data" %>
    <%= f.file_field :image, class: "upload-file" %>
<% end %>

<div class="upload-preview">
  <%= image_tag @photo.image_url.to_s, height: "300" %>

In your controller make sure to allow the attachment param:

# app/controllers/photos_controller.rb

class PhotosController < ApplicationController
  # ...
  def create
    @photo =

      redirect_to @photo
      render :new
  # ...


  def photo_params
    params.require(:photo).permit(..., :image) # permit attachment param

Now you should have working synchronous file uploads.

6. Direct upload

We can now add asynchronous direct uploads to the mix. We'll be using Uppy and its XHRUpload plugin, which will upload selected files to Shrine's upload endpoint.

6a. Upload endpoint

We'll first configure the upload_enpdoint plugin and mount it in our routes:

# config/initializers/shrine.rb
# ...
Shrine.plugin :upload_endpoint, url: true
# config/routes.rb

Rails.application.routes.draw do
  # ...
  mount Shrine.upload_endpoint(:cache) => "/upload"

6b. Uppy

Now we can setup Uppy to do the direct uploads. First we'll add the package to our bundle (we're assuming you're using webpacker):

$ yarn add uppy

Now we can setup direct uploads, where selected files will go to Shrine's upload endpoint, and upload result will be written to the hidden attachment field:

// app/javascript/fileUpload.js

import 'uppy/dist/uppy.min.css'

import {
} from 'uppy'

function fileUpload(fileInput) {
  const hiddenInput = document.querySelector('.upload-data'),
        imagePreview = document.querySelector('.upload-preview img'),
        formGroup = fileInput.parentNode

  // remove our file input in favour of Uppy's

  const uppy = Core({
      autoProceed: true,
    .use(FileInput, {
      target: formGroup,
    .use(Informer, {
      target: formGroup,
    .use(ProgressBar, {
      target: imagePreview.parentNode,
    .use(ThumbnailGenerator, {
      thumbnailHeight: 600,
    .use(XHRUpload, {
      endpoint: '/upload', // path to the upload endpoint

  uppy.on('thumbnail:generated', (file, preview) => {
    // show image preview while the file is being uploaded
    imagePreview.src = preview

  uppy.on('upload-success', (file, response) => {
    // retrieve uploaded file data
    const uploadedFileData = response.body['data']

    // set hidden field value to the uploaded file data so that it's submitted
    // with the form as the attachment
    hiddenInput.value = JSON.stringify(uploadedFileData)

export default fileUpload
// app/javascript/packs/application.js
// ...
import fileUpload from 'fileUpload'

// listen on 'turbolinks:load' instead of 'DOMContentLoaded' if using Turbolinks
document.addEventListener('DOMContentLoaded', () => {
  document.querySelectorAll('.upload-file').forEach(fileInput => {

And add the following CSS:

/* app/assets/stylesheets/application.css */
/* ... */
.upload-preview img {
  display: block;
  max-width: 100%;

.upload-preview {
  margin-bottom: 10px;
  display: inline-block;
  height: 300px;

img[src=""] {
  visibility: hidden;

And that's it, now when a file is selected it will be asynchronously uploaded directly to S3, accompanied by an image preview and a nice progress bar.

See also