# edit call partial _form.haml, from _form, in the loop for photo shows, render a partial call: _photo_fields
# here is a part of _form.haml:
= simple_form_for @travail, remote: true do |article|
  .
  .
  .
    %h3 Photos
    #photos
      = article.simple_fields_for :photos do |photo|
        = render partial: 'photo_fields', locals: { f: photo }
      %div{ :style => "display: block; position: relative; clear: both;"}
        %br= link_to_add_association 'add photo', article, :photos
  .actions
    = article.button :magic_submit, cancel: travails_path

# here is _photo_fields.haml
.nested-fields
  %hr
  .col-md-5
    = f.hidden_field :retained_photo
    = f.input :photo, as: :file, label: "Add a photo", class: "upload", :input_html => { onchange: "readURL(this);" }
    - if f.object.photo
      = image_tag(f.object.photo.thumb('140x140!').url, alt: f.object.title, class: 'preview')
    - else
      %img.preview
  .col-md-7
    = f.input :title
    = f.input :description
  = link_to_remove_association 'remove', f

#here is important part of my controller: travails_controller.rb:
class TravailsController < ApplicationController
  before_action :set_travail, only: [:show, :edit, :update, :destroy]
  before_action :authenticate_user!, only: [:edit, :update, :destroy, :create, :new]
  before_action :role_required,  except: [ :index, :show ]


  private
    def set_travail
      @travail = Travail.find(params[:id])
    end

    def travail_params
      params.require(:travail).permit(:title, :description, :content, :location, :company,
                                      :user_id, :image, :wconcern_id,
                                      photos_attributes: [:id, :title, :categorie,
                                                          :description, :photo, :_destroy])
    end
end

# this is important part of my model for Travail: travail.rb
class Travail < ActiveRecord::Base

  has_many :photos
  accepts_nested_attributes_for :photos, :allow_destroy => true


end

# part of my photo.rb model:
class Photo < ActiveRecord::Base
  belongs_to :travail


end