This plugin for Merb and Rails provides a simple and extremely flexible way to upload files.
Install the latest stable release:
[sudo] gem install carrierwave
Or the cutting edge development version:
[sudo] gem install jnicklas-carrierwave --source http://gems.github.com
In Merb, add it as a dependency to your config/dependencies.rb:
In Rails, add it to your environment.rb:
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 include CarrierWave::Uploader storage :file end
You can use your uploader class to store and retrieve files like this:
uploader = AvatarUploader.new uploader.store!(my_file) uploader.retrieve_from_store!('my_file.png')
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
First require the relevant extension:
require 'carrierwave/orm/activerecord' require 'carrierwave/orm/datamapper' require 'carrierwave/orm/sequel'
You don't need to do this if you are using Merb or Rails.
Open your model file, for ActiveRecord do something like:
class User < ActiveRecord::Base mount_uploader :avatar, AvatarUploader end
Or for DataMapper:
class User include DataMapper::Resource mount_uploader :avatar, AvatarUploader end
Or for Sequel
class User < Sequel::Model mount_uploader :avatar, AvatarUploader end
Now you can cache files by assigning them to the attribute, they will automatically be stored when the record is saved.
u = User.new u.avatar = params[:file] u.avatar = File.open('somewhere') u.save! 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 include CarrierWave::Uploader def store_dir 'public/my/upload/directory' end end
This works for the file storage as well as Amazon S3.
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 include CarrierWave::Uploader include CarrierWave::RMagick process :resize => [800, 800] version :thumb do process :crop_resized => [200,200] end end
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 = AvatarUploader.new uploader.store!(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 include CarrierWave::Uploader version :animal do version :human version :monkey version :llama end end
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| %> <p> <label>My Avatar</label> <%= f.file_field :avatar %> <%= f.hidden_field :avatar_cache %> </p> <% 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| %> <p> <label>My Avatar</label> <%= image_tag(@user.avatar.url) if @user.avatar %> <%= f.file_field :avatar %> <%= f.hidden_field :avatar_cache %> </p> <% end %>
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 include CarrierWave::Uploader storage :s3 end
That's it! You can still use the +CarrierWave::Uploader#url+ method to return the url to the file on Amazon S3
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 include CarrierWave::Uploader include CarrierWave::RMagick end
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 include CarrierWave::Uploader include CarrierWave::RMagick process :crop_resized => [200, 200] process :convert => 'png' def filename super + '.png' end end
Check out the manipulate! method, which makes it easy for you to write your own manipulation methods.
ImageScience works the same way as RMagick.
class AvatarUploader include CarrierWave::Uploader include CarrierWave::ImageScience process :crop_resized => [200, 200] end
Full rdoc documentation is available at Rubyforge.
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.