activeAdmin, carrierwave, has_many files, reject_if attributes NOT present, allow_destroy

suit.rb

require "babosa"

class Suit < ActiveRecord::Base
  has_and_belongs_to_many :complects
  has_and_belongs_to_many :special_props
  has_many :checkins, :dependent => :destroy
  has_many :items, :through => :checkins

  has_many :suit_photos
  accepts_nested_attributes_for :suit_photos,
                                :reject_if => lambda { |attributes|
                                  # puts "----------------------"
                                  # puts attributes
                                  # puts "----------------------"
                                  # attributes[:filename].blank?
                                  !attributes.present?
                                },
                                :allow_destroy => true

  extend FriendlyId
  friendly_id :title, use: :slugged

  def normalize_friendly_id(input)
    input.to_s.to_slug.normalize(transliterations: :russian).to_s
  end

end

https://gist.github.com/c80609a/e64ff4f3dcc7ee8a2b86