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A Rails engine which takes care of creating Attachments using the jQuery File Upload plugin.
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A Rails engine for creating Attachments using the jQuery File Upload plugin.



Add this line to your application's Gemfile:

gem 'simple_form_attachments'

And then execute:

$ bundle

Or install it yourself as:

$ gem install simple_form_attachments

Add simple_form_attachments to application.js:

//= require simple_form_attachments


Attachment model

Create a model for your attachments that includes the SimpleFormAttachments::Attachment concern:

class AttachmentImage
  include SimpleFormAttachments::Attachment

This adds a :temporary Boolean field (set to false by default) and two scopes: temporary and permanent to the model.

Note that the concern does not include any specific accessors (ie Dragonfly). You need to define those yourself in your model.


Standard Rails validation errors are displayed in the uploader, should the uploaded file not pass the validations defined on the attachment model.

Owner model

Add the SimpleFormAttachments::HasAttachments concern to the attachment owner. This includes the mongoid relation macros has_one_attachment and has_many_attachments:

class Parent
  include Mongoid::Document
  include SimpleFormAttachments::HasAttachments

  has_one_attachment :attachment_pdf, class_name: 'AttachmentPdf'
  has_many_attachments :attachment_images, class_name: 'AttachmentImage'

Relations between the parent and Attachment are referenced, not embedded. The gem uses belongs_to for 1–1 relations and has_and_belongs_to_many for 1–n relations. This is to ensure that relations work with embedded parents, since the relations need to be stored on the owner's side.

You could use for example the before_save callback to embed the attachments yourself.


Since attachments can be added/removed dynamically in the form, we need to indicate which ones are actually submitted in the end, so that we can – immediately or later (left up to you) – delete the temporary ones.

For that each relation defines a method named after the relation name, which can be called for example via a callback:

after_save :mark_attachment_pdf_permanent
after_save :mark_attachment_images_permanent

These methods (atomically) set the attachment's :temporary attribute to false.

Alternatively the mark_all_attachments_permanent method can be used to loop through all attachment relations, triggering individual above-mentioned methods. This means the two after_save callbacks above can be replaced with:

after_save :mark_all_attachments_permanent


If you want to validate the number of attachments allowed on the owner, you can use for example the following validation. Eventual validation errors will be displayed to the user when submitting the parent form.

validates :attachment_pdfs, length: { maximum: 2 }


The default UploadController receives the uploaded attachment, sets its temporary to true and creates corresponding record in the database.

Remember, you need to mark attachments as permanent (ie temporary to false) yourself. See Callbacks above.


Mount the engine in your routes:

mount SimpleFormAttachments::Engine => "/"

This will include a default /attachments route.


Now you can use the attachment input in your SimpleForm forms:

= form.input :attachment_images, as: :attachment



Sorting of attachments is turned on by default for has_many_attachments relations. But it's possible to disable sorting on a field:

= f.input :attachment_images, as: :attachment, sortable: false


Uploaded attachments are displayed in a div. The gem will look for a partial using the normal rails partial lookup (with a fallback to the default partial), this makes it easy to define a partial for each of your attachment models.

Here an example partial for a model called AttachmentImage:

/ app/views/simple_form_attachments/attachment_images/_attachment_image.html.slim
/ (Note the nesting in 'simple_form_attachments' directory.)

div class=SimpleFormAttachments.dom_class(:attachment, [:col, :thumb])
  = image_tag attachment.thumb_url

div class=SimpleFormAttachments.dom_class(:attachment, [:col, :file_info])
  span class=SimpleFormAttachments.dom_class(:attachment, :col, :file_info, :name)
    = link_to attachment.file_name, attachment.file.url
  span class=SimpleFormAttachments.dom_class(:attachment, :col, :file_info, :mime_type)
    = attachment.file_mime_type
  span class=SimpleFormAttachments.dom_class(:attachment, :col, :file_info, :size) data-filesize=attachment.file_size
    = attachment.file_size

- if attachment.errors.to_a.any?
  div class=SimpleFormAttachments.dom_class(:attachment, [:col, :errors])
    = render 'simple_form_attachments/errors', errors: attachment.errors.to_a

- else
  div class=SimpleFormAttachments.dom_class(:attachment, [:col, :fields])
    = fields.input :caption

Dom class and CSS

The component is isolated in the simple_form_attachments namespace. This gem comes with its own helper that generates corresponding class names – for example SimpleFormAttachments.dom_class(:attachment, :file_info) would generate simple_form_attachments__file_info.

Basic styling can be achieved by including simple_form_attachments css in your app:

*= require simple_form_attachments

Validation errors

If you want to show validation errors in your partial, simply include the simple_form_attachments/errors partial as shown above.


You can customize the engine to use a different controller and route, for example should you want to preprocess the uploaded files or determine the attachment model based on file mime/extension/format, ….

Setup a controller for your attachments:

class AttachmentsController < SimpleFormAttachments::UploadController
  # The default controller uses the attachment type passed from the form input
  # to determine which Attachment class to create.
  # This can be easily overridden, for instance if you want to infer
  # the class from the `mime type` of the file:
  def attachment_class
    mime_type = params[:attachment][:file].content_type

Add route as usual:

resources :attachments, only: [:create]

Specify the route either app wide in an initializer:

# config/initializers/simple_form_attachments.rb

require 'simple_form_attachments'
# Configuration

SimpleFormAttachments::AttachmentInput.configure do |c|
  c.route = attachments_path
  # can be also specified as a lambda to be evaluated at runtime: -> { attachments_path }

Or per input:

= f.input :attachment_images, as: :attachment, route: attachments_path


Besides a MiniTest test suite, the gem has a dummy app located at test/dummy. Simply cd into the directory and run bin/rails s to test the uploader.


  1. Fork it ( )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request