carrierwave.md

CarrierWave and S3

CarrierWave is a gem that adds a fairly simple and flexible way to users to upload files to our Rails application. It also lets us resize images to make thumbnails and other sizes as we need them, and lets us upload all these uploaded (and generated) files to cloud storage products, such as S3.

How-to

Make an S3 bucket

S3 -- Simple Storage Service "buckets" are like folders

---

Let's start with a new Rails app

$ rails new band_practice
$ cd band_practice
$ rails g scaffold band name genre
$ rake db:migrate

Setup Carrierwave and Fog Gems

Fog is a gem that helps us work with cloud services like those from Amazon - EC2 or S3 - as well as cloud offerings from other companies (like Microsoft, Rackspace, Blue Box, etc).

gem 'carrierwave'
gem 'fog'
gem 'dotenv-rails'

Add an Uploader

Now you need a uploader. This is the file which has all the settings like which folder the image will be saved, setting the image quality, caching etc.

$ rails g uploader image

The generator creates a new directory called uploaders under the app directory and in it a file called image_uploader.rb. In this file are a number of comments explaining how to customize the uploader. For example there is code to change the upload location, perform processing on the image after uploading and to restrict the type of files that can be uploaded. You should take a look at these options on your own, but for demonstration purposes we're going to get rid of most of it in favor of this:

class ImageUploader < CarrierWave::Uploader::Base
  include CarrierWave::MiniMagick

  def store_dir
    "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end

  version :thumb do
    process :resize_to_fit => [32, 32]
  end

  version :preview do
    process :resize_to_fit => [256, 256]
  end

  version :full do
    process :resize_to_fit => [2048, 2048]
  end
end

Next we'll need to add the uploader to the Band model. We'll need a column in the bands table to store it in so we'll generate a migration to do add it.

 $ rails g migration add_image_to_bands image:string
 $ rake db:migrate

Then, we mount the uploader on the Band model.

class Band < ActiveRecord::Base
  mount_uploader :image, ImageUploader
end

Add a file_field to the Band form.

app/views/bands/_form.html.erb

<div class="field">
  <%= f.label :image %><br>
  <%= f.file_field :image %>
</div>

We add :image to the strong params for the controller.

app/controllers/bands_controller.rb

def band_params
  params.require(:band).permit(:name, :genre, :image)
end

Finally, we modify the scaffolded form and show pages to include a form element for the image upload, and modify the form_for to add an :html option.

apps/views/bands/show.html.erb

<p>
  <%= image_tag @band.image_url.to_s %>
</p>

Now we can upload images - yay! In your terminal, take a look at public/uploads - mini_magick and carrierwave made all those files for us! We have access to these different sizes by passing the symbol of the size (as defined in our uploader model) to #image_url

app/views/bands/show.html.erb

<p>
  <%= image_tag @band.image_url(:thumb).to_s %>
</p>

Uploading to S3

This is cool, but we want to save to S3 instead of the local file system. This is pretty easy. First, we need to tell CarrierWave that we want to use S3. Make a new initializer, config/initializers/carrierwave.rb

CarrierWave.configure do |config|
  config.fog_credentials = {
    provider:               'AWS',
    aws_access_key_id:      ENV['S3_KEY'],
    aws_secret_access_key:  ENV['S3_SECRET'],
  }

  # For testing, upload files to local `tmp` folder.
  if Rails.env.test? || Rails.env.cucumber?
    config.storage           = :file
    config.enable_processing = false
    config.root              = "#{Rails.root}/tmp"
  else
    config.storage = :fog
  end

  config.cache_dir        = "#{Rails.root}/tmp/uploads" # To let CarrierWave work on Heroku
  config.fog_directory    = ENV['S3_BUCKET_NAME']
end

We also need to fill out our config/application.yml file. We can get the secret information from the Security Credentials screen in the AWS dashboard - I won't go into how to fetch this information here, as its likely to change from time to time.

Resources

Railscasts #253 CarrierWave File Uploads

Railscasts #383 Uploading to Amazon S3

Allowing File Uploads with CarrierWave

Saving files in Amazon S3 using Carrierwave and Fog Gem