CarrierWave Cheatsheet

The CarrierWave gem provides us with an easy way to allow file uploads through forms.

Installation

In your Gemfile, include

gem 'carrierwave'

and then bundle install.

Getting Started

Add a column to store the file's URL

You need to have a column of type "string" in whichever table that you want to attach a file upload to. This column will, ultimately, store the URL of the uploaded file after CarrierWave hosts it.

If you already included the column when you generated your resource, great. Skip to the next step.

If not, you have to add it. For example, here we add a column called "avatar" to users, which we plan to store an image in:

rails generate migration add_avatar_to_users avatar:string
rake db:migrate

In your case, it may be song, transcript, image, etc.

Generate an uploader

From the command line:

rails generate uploader Avatar

In your case, change "Avatar" to match whatever you are trying to upload / the column you added to the table: Song, Transcript, Image, etc.

Restart your rails server.

Mount the uploader in the model

In the relevant model,

# app/models/user.rb
class User < ActiveRecord::Base
  mount_uploader :avatar, AvatarUploader
end

Again, customize to match your use case. :avatar should be the column you created, and AvatarUploader should be whatever you generated.

Enhance the form

We need an <input type="file"> in our form to handle the upload. If you already have a type="text" input, change it; or if you don't, add a new one:

<input type="file" id="avatar" name="avatar" class="form-control">

If you are customizing a Devise form, it would instead look like <%= f.file_field :avatar, :class => "form-control" %>.

We also need to change the <form> tag itself to allow files to be uploaded by adding the enctype="multipart/form-data" attribute:

 <form action="/create_user" method="post" class="form-horizontal" enctype="multipart/form-data">

If you are customizing a Devise form, it would instead look like <%= form_for(resource, as: resource_name, url: registration_path(resource_name), :html => { :multipart => true }) do |f| %>.

Assign the file just like any other params

In your create/update actions, assign the new file upload just like any other form parameter:

@user.avatar = params[:avatar]

If you are customizing a Devise form, you'll have to instead allow this additional parameter through security.

That should be it!

Retrieving the upload

CarrierWave will, by default, process the upload and then store it in your public folder, so that you can use it just like any other URL on the internet.

For example, we could now do

   <img src="<%= user.avatar %>" class="img-responsive">

Adding Cloudinary for storage

CarrierWave works fine locally at this point, but it's going to break if you try to host your project live on Heroku. That's because Heroku won't let you permanently write to the public folder of a live application. You'll need to find a hosting service, like Amazon AWS to host any uploaded files. Fortunately, Cloudinary makes it easy to host uploaded images and they have a generous free tier. To integrate Cloudinary, first add the following line to your Gemfile:

gem "cloudinary"

and in terminal, run:

bundle install

Then adjust your ImageUploader file so it looks like:

class ImageUploader < CarrierWave::Uploader::Base
  include Cloudinary::CarrierWave
end

To get Cloudinary fully integrated, you'll need to sign up for an account and get your API info. You can find your cloud name, by going to Settings and clicking the Account tab. You can find your API key and secret by going to Settings and clicking the Security tab.

For security, it's best to store your keys in environment variables. If you're using dotenv, you can create a file called .env in the root folder of your app. Then add the following content to the .env file, replacing your information as needed:

CLOUDINARY_CLOUD_NAME="replace me with your cloud name"
CLOUDINARY_API_KEY="replace me with your api key"
CLOUDINARY_API_SECRET="replace me with your api secret"

After pushing to Heroku, you'll need to manually add these environment variables in the Settings tab of your application.

Finally, create an initializer file called cloudinary.rb in config/initializers and add the following content:

Cloudinary.config do |config|
  config.cloud_name = ENV["CLOUDINARY_CLOUD_NAME"]
  config.api_key = ENV["CLOUDINARY_API_KEY"]
  config.api_secret = ENV["CLOUDINARY_API_SECRET"]
  config.cdn_subdomain = true
end

arjunvenkat/carrierwave.md