CarrierWave
This plugin for Merb and Rails provides a simple and extremely flexible way to upload files.
Getting Started
At the moment you are going to have to grab it here from github and install it yourself.
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:
app/uploaders/avatar_uploader.rb
Check out this file for some hints on how you can customize your uploader. It should look something like this:
class AvatarUploader < 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
First require the activerecord extension:
require 'carrierwave/orm/activerecord
You don't need to do this if you are using Merb or Rails.
Open your model file, and do something like:
class User < ActiveRecord::Base
mount_uploader :avatar, AvatarUploader
end
Now you can upload files!
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'
DataMapper
First require the activerecord extension:
require 'carrierwave/orm/datamapper
You don't need to do this if you are using Merb or Rails.
Open your model file, and do something like:
class User
include DataMapper::Resource
mount_uploader :avatar, AvatarUploader
end
Now you can upload files!
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 < CarrierWave::Uploader
def store_dir
'public/my/upload/directory'
end
end
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
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.
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 %>
What's in that uploader file?
The fact that uploaders are separate classes in CarrierWave is a big advantage. What this means for you is:
Less magic
In order to customize your uploader, all you need to do is override methods and use normal, clear and simple Ruby code. That means no alias_method_chain
'ing to hook into the upload process, no messing around with weird extensions. The code in CarrierWave is very simple and easy because of this.
Easier to test
How do you test file uploads? I always found this ridiculously hard. A separate class means you can test is separately, which is nicer, easier and more maintainable.
More Flexible
Many of the things you can do in CarrierWave are hard, or impossible to do in other file upload plugins, and have previously required you to roll your own. Now you can get all the flexibility without having to write low level stuff.
Easy to extend
CarrierWave has support for a few different image manipulation libraries. These need no code to hook into CarrierWave, because they are simple modules. If you want to write your own manipulation library (doesn't need to be for images), you can do the same.
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 < 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
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. It's not loaded by default so you'll need to require it:
require 'carrierwave/processing/rmagick'
You'll also need to include it in your Uploader:
class AvatarUploader < 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 < 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.
Using ImageScience
ImageScience works the same way as RMagick. As with RMagick you'll need to require it:
require 'carrierwave/processing/image_science'
And then include it in your model:
class AvatarUploader < CarrierWave::Uploader
include CarrierWave::ImageScience
process :crop_resized => [200, 200]
end
Read the source
CarrierWave is still young, but most of it is pretty well documented. Just dig in and look at the source for more in-depth explanation of what things are doing.