Started POST "/item/create" for 127.0.0.1 at 2018-10-23 13:08:19 +0300
Processing by ItemsController#create as HTML
Parameters: {"utf8"=>"✓","authenticity_token"=>
"tDpyPV9fPxLUHgRVb4G6P3eMLFUv0hKVnNPJCAcgYISCwjIbjA5bu/iXOy0k6yL
8+QWXs3MyoJ3lzzyhj3rqkw==", "item"=>{"title"=>"Sample",  "description"
=>"Lorem", "attachments_attributes"=>{"0"=>{"media_files"=>[#
<ActionDispatch::Http::UploadedFile:0x007fe818a5ecb0 @tempfile=#
<Tempfile:/var/folders/hq/pr4rt14n7s31v3f6292wtjm00000gn/T/
RackMultipart20181023-1573-1r65sf9.jpg>, @original_filename=
"image1.jpg", @content_type="image/jpeg", @headers="Content-
Disposition: form-data; name="item[attachments_attributes]
[0][media_files][]"; filename="image1.jpg"rnContent-Type:
image/jpegrn">, #<ActionDispatch::Http::UploadedFile
:0x007fe818a5ebe8 @tempfile=#
<Tempfile:/var/folders/hq/pr4rt14n7s31v3f6292wtjm00000gn
/T/RackMultipart20181023-1573-1lbr709.jpg>,
@original_filename="image2.jpg", @content_type=
"image/jpeg", @headers="Content-Disposition: form-data;
name="item[attachments_attributes][0][media_files][]";
filename="image2.jpg"rnContent-Type: image/jpegrn">], "item_id"=>"#
<Item:0x007fe813ef65e8>"}}}, "commit"=>"Create"}

Unpermitted parameter: :media_files

create_table "attachments", force: :cascade do |t|
  t.integer "item_id"
  t.string "media_files"
  t.string "content_type"
  t.datetime "created_at", null: false
  t.datetime "updated_at", null: false
end

class Item < ApplicationRecord
  has_many :attachments, dependent: :destroy
  accepts_nested_attributes_for :attachments, allow_destroy: true
end

class Attachment < ApplicationRecord
  belongs_to :item
  mount_uploader :media_files, AttachmentUploader
  validates_presence_of :media_files
end

def create
  params["item"]["attachments_attributes"]["0"]["media_files"].each { |file| @attachment = Attachment.new(:media_files => file)}

  respond_to do |format|
    if @attachment.save
      format.html { redirect_back fallback_location: root_path, notice: 'Attachment was successfully created.' }
      format.json { render :'shows/show', status: :created, location: @attachment }
    else
      format.html { render :new }
      format.json { render json: @attachment.errors, status: :unprocessable_entity }
    end
  end
end

params.require(:item).permit(:title, :description, attachments_attributes: [:media_files, :item_id, :content_type])

<%= form_for(@item, url: items_create_path, :html => { :multipart => true }) do |form| %>
<%= form.text_field :title, id: :item_title, autofocus: true, :class=>"form-control" %>
    <%= form.text_area :description, id: :item_description, :class=>"form-control" %>

  <%= form.fields_for :attachments do |f| %>
      <div class="form-group">
  <%= f.file_field :media_files, multiple: true, :id=>"upload-photo" %>
  <% end %>

  <%= form.submit "Create", :class=>"btn btn-default" %>
  <% end %>