NestedForm + CarrierWave

gistfile1.slim

= nested_form_for answer, remote: true, ... do |f|
  ...
  = f.fields_for :attachments do |attachment_form|
    - if attachment_form.object.file.present?
      p = attachment_form.object.file.identifier
    - else
      = attachment_form.label :file
      = attachment_form.file_field :file
    = attachment_form.link_to_remove "Remove this file"
  = f.link_to_add "Add file", :attachments
  = f.submit