refile multiply file upload

_form.html.slim

= semantic_nested_form_for @gallery, multipart: true do |form|
  = form.input :file_multiple, as: :file, input_html: { multiple: true }

  = form.actions do
    = form.action :submit

galleries_controller.rb

class GalleriesController < SpotControllerBase
  # some code ...
  
  def update
    if @gallery.update_attributes(params[:gallery])
      create_multiple_files(:gallery, @gallery)
      redirect_to gallery_path(@gallery)
    else
      render action: "edit"
    end
  end

  def create
    @gallery = Gallery.create!(params[:gallery])
    create_multiple_files(:gallery, @gallery)
    redirect_to gallery_path(@gallery)
  end

  private

  def create_multiple_files(parent, record)
    multiple = params[parent][:file_multiple]
    multiple.each { |file| record.photos.create! file: file }
  end
end

gallery.rb

class Gallery < ActiveRecord::Base
  has_many :photos, dependent: :destroy

  attr_accessor :file_multiple

  accepts_nested_attributes_for :photos, allow_destroy: true
end

photo.rb

class Photo < ActiveRecord::Base
  belongs_to :gallery

  attachment :file

  before_validation :generate_file_filename

  private

  def generate_file_filename
    extension = self.file_content_type == nil ? '' : Rack::Mime::MIME_TYPES.invert[self.file_content_type]
    filename = self.gallery.nil? || self.gallery.title.blank? ? 'photo' : self.gallery.title.parameterize
    self.file_filename = "#{filename}#{extension}"
  end
end