Multiple files upload with carrierwave and nested_form

I wrote this post just to show how it’s possible to get a perfectly working form with multiple files upload within a few minutes. If you need to implement multiple file attachments to a given object with only one form quickly, this example could help you.

So let’s create an example project (I used one of mine rails templates_:

rails new carrierwave-nested_form -d mysql -m rails-templates/jquery.rb

Then add the gems to Gemfile:

gem 'carrierwave', '>= 0.5.3'

gem 'nested_form'

The specified version for carrierwave is required because there is a small bug in the previous versions of carrierwave that creates some problems with nested forms.

In this example, I chose to use two simple models related with a polymorphic association. In order to do that, let’s create the two model objects:

rails generate model article title:string description:text
rails generate model attachment description:text file:string attachable:references

You have to add the polymorphic option to the migration for the attachments before executing it.

Now that we have the two model objects, we install the nested_form gem files in our project:

rails g nested_form:install

This gem is very nice because it gives you the opportunity to create nested forms with nice javascript add/remove links with a minimum effort. Before proceeding with the nested form, please remember to add the javascript to your layout:

<%= javascript_include_tag :defaults,"nested_form" %>

So we are ready to create a carrierwave uploader:

rails generate uploader file

and mount the uploader to the chosen field of the attachment model:

class Attachment < ActiveRecord::Base
attr_accessible :description, :file

belongs_to :attachable, :polymorphic => true

mount_uploader :file, FileUploader

Practically, a carrierwave uploader is a class that handles a certain type of uploading in your model. You just need to mount the uploader of a string field of your model. This is a very good design decision because it gives you a lot of flexibility, for example, when you want to share the same uploading features between two models.

Now, we are ready to add the nested feature to the article form. So let’s proceed in the following order:

class Article < ActiveRecord::Base
attr_accessible :title, :description, :attachments_attributes

has_many :attachments, :as => :attachable

accepts_nested_attributes_for :attachments

You have to pay attention to the attr_accessible for attacchments_attributes. It won’t work if you don’t add that field to the list of accessible ones. And eventually we modify the form in the following way:

<%= nested_form_for @article, :html=>{:multipart => true } do |f| %>
<%= f.error_messages %>

  <%= f.label :title %><br />
  <%= f.text_field :title %>
  <%= f.label :description %><br />
  <%= f.text_area :description %>
  <%= f.fields_for :attachments do |attachment_form|  %>
    <%= attachment_form.label :description %><br />
    <%= attachment_form.text_area :description %>
    <%= attachment_form.label :file %><br />
    <%= attachment_form.file_field :file %>
    <%= attachment_form.link_to_remove "Remove this attachment" %>
  <% end %>
  <%= f.link_to_add "Add attachment", :attachments %>
  <p><%= f.submit %></p>
 <% end %>

And we’re done!

I have created a demo app just in case you want to play with it a bit.