Classier solution for file uploads for Rails, Sinatra and other Ruby web frameworks
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This plugin for Merb and Rails provides a simple and extremely flexible way to upload files.

Getting Started

Install the latest stable release:

[sudo] gem install carrierwave

Or the cutting edge development version:

[sudo] gem install jnicklas-carrierwave --source

In Merb, add it as a dependency to your config/dependencies.rb:

dependency 'carrierwave'

In Rails, add it to your environment.rb:

config.gem "carrierwave"

Quick Start

Start off by generating an uploader:

merb-gen uploader Avatar

or in Rails:

script/generate uploader Avatar

this should give you a file in:


Check out this file for some hints on how you can customize your uploader. It should look something like this:

class AvatarUploader < CarrierWave::Uploader::Base
  storage :file

You can use your uploader class to store and retrieve files like this:

uploader =!(my_file)


CarrierWave gives you a store for permanent storage, and a cache for temporary storage. You can use different stores, at the moment a filesystem store and an Amazon S3 store are bundled.

Most of the time you are going to want to use CarrierWave together with an ORM. It is quite simple to mount uploaders on columns in your model, so you can simply assign files and get going:

ActiveRecord, DataMapper, Sequel

If you are not using Merb or Rails you'll need to require the relevant ORM extension.

require 'carrierwave/orm/activerecord'
require 'carrierwave/orm/datamapper'
require 'carrierwave/orm/sequel'

Open your model file, for ActiveRecord do something like:

class User < ActiveRecord::Base
  mount_uploader :avatar, AvatarUploader

Or for DataMapper:

class User
  include DataMapper::Resource

  mount_uploader :avatar, AvatarUploader

Or for Sequel

class User < Sequel::Model
  mount_uploader :avatar, AvatarUploader

Now you can cache files by assigning them to the attribute, they will automatically be stored when the record is saved.

u =
u.avatar = params[:file]
u.avatar ='somewhere')!
u.avatar.url # => '/url/to/file.png'
u.avatar.current_path # => 'path/to/file.png'

Changing the storage directory

In order to change where uploaded files are put, just override the store_dir method:

class MyUploader < CarrierWave::Uploader::Base
  def store_dir

This works for the file storage as well as Amazon S3.

Adding versions

Often you'll want to add different versions of the same file. The classic example is image thumbnails. There is built in support for this:

class MyUploader < CarrierWave::Uploader::Base
  include CarrierWave::RMagick

  process :resize => [800, 800]

  version :thumb do
    process :crop_resized => [200,200]


When this uploader is used, an uploaded image would be scaled to be no larger than 800 by 800 pixels. A version called thumb is then created, which is scaled and cropped to exactly 200 by 200 pixels. The uploader could be used like this:

uploader =!(my_file)                              # size: 1024x768

uploader.url # => '/url/to/my_file.png'               # size: 800x600
uploader.thumb.url # => '/url/to/thumb_my_file.png'   # size: 200x200

One important thing to remember is that process is called before versions are created. This can cut down on processing cost.

It is possible to nest versions within versions:

class MyUploader < CarrierWave::Uploader::Base

  version :animal do
    version :human
    version :monkey
    version :llama

Making uploads work across form redisplays

Often you'll notice that uploaded files disappear when a validation fails. CarrierWave has a feature that makes it easy to remember the uploaded file even in that case. Suppose your user model has an uploader mounted on avatar file, just add a hidden field called avatar_cache. In Rails, this would look like this:

<% form_for @user do |f| %>
    <label>My Avatar</label>
    <%= f.file_field :avatar %>
    <%= f.hidden_field :avatar_cache %>
<% end %>

It might be a good idea to show th user that a file has been uploaded, in the case of images, a small thumbnail would be a good indicator:

<% form_for @user do |f| %>
    <label>My Avatar</label>
    <%= image_tag(@user.avatar.url) if @user.avatar %>
    <%= f.file_field :avatar %>
    <%= f.hidden_field :avatar_cache %>
<% end %>

NOTE: this feature currently requires write access to your filesystem. If write access is unavailable you will not be able to upload files. You can prevent CarrierWave from writing to the file system by setting `CarrierWave.config = false`. This will however break redisplays of forms.

Providing a default path

In many cases, especially when working with images, it might be a good idea to provide a default path, a fallback in case no file has been uploaded. You can do this easily by overriding the default_path method in your uploader:

class MyUploader < CarrierWave::Uploader::Base
  def default_path
    "images/fallback/" + [version_name, "default.png"].compact.join('_')

Using Amazon S3

You'll need to configure a bucket, access id and secret key like this:

CarrierWave.config[:s3][:access_key_id] = 'xxxxxx'
CarrierWave.config[:s3][:secret_access_key] = 'xxxxxx'
CarrierWave.config[:s3][:bucket] = 'name_of_bucket'

Do this in an initializer in Rails, and in a before_app_loads block in Merb.

And then in your uploader, set the storage to :s3

class AvatarUploader < 
  storage :s3

That's it! You can still use the +CarrierWave::Uploader#url+ method to return the url to the file on Amazon S3

Using RMagick

If you're uploading images, you'll probably want to manipulate them in some way, you might want to create thumbnail images for example. CarrierWave comes with a small library to make manipulating images with RMagick easier, you'll need to include it in your Uploader:

class AvatarUploader < CarrierWave::Uploader::Base
  include CarrierWave::RMagick

The RMagick module gives you a few methods, like +CarrierWave::RMagick#crop_resized+ which manipulate the image file in some way. You can set a process callback, which will call that method any time a file is uploaded.

class AvatarUploader < CarrierWave::Uploader::Base
  include CarrierWave::RMagick

  process :crop_resized => [200, 200]
  process :convert => 'png'

  def filename
    super + '.png'

Check out the manipulate! method, which makes it easy for you to write your own manipulation methods.

Using ImageScience

ImageScience works the same way as RMagick.

class AvatarUploader < CarrierWave::Uploader::Base
  include CarrierWave::ImageScience

  process :crop_resized => [200, 200]


If you are using Paperclip, you can use the provided compatibility module:

class AvatarUploader < CarrierWave::Uploader::Base
  include CarrierWave::Compatibility::Paperclip

See the documentation for +Paperclip::Compatibility::Paperclip+ for more detaills.

Be sure to use mount_on to specify the correct column:

mount_uploader :avatar, AvatarUploader, :mount_on => :avatar_file_name

Unfortunately AttachmentFoo differs too much in philosophy for there to be a sensible compatibility mode. Patches for migrating from other solutions will be happily accepted.


The activerecord validations use the Rails i18n framework. Add these keys to your translations file:

    integrity: 'Not an image.'
    processing: 'Cannot resize image.'


These people have contributed their time and effort to CarrierWave:

  • Jonas Nicklas

  • Pavel Kunc


MIT-License, see the separate LICENSE file in the source distribution.

Read the source

CarrierWave is still young, but most of it is pretty well documented. It is also extensively specced, and there are cucumber features for some common use cases. Just dig in and look at the source for more in-depth explanation of what things are doing.