edit.html.haml

.container.proto-new
  = form_for @prototype do |f|
    = f.hidden_field :user_id, value: current_user.id
    .col-md-8.col-md-offset-2
      %header.row.user-nav.row
        .col-md-12
          %h4 Title
          .proto-new-title
            = f.text_field :title, required: true, autofocus: true, placeholder: "Input Title"
      .row
        .col-md-12
          %h4 Main Thumbnail
          .cover-image-upload#main_image_uploader
            = f.fields_for :captured_images do |image|
              %img#selected_image
              = image.file_field :content
              = image.hidden_field :status, value: "main"
        .col-md-12
          %h4 Sub Thumbnails
          %ul.proto-sub-list.list-group
            - 3.times do |i|
              %li.list-group-item.col-md-4
                .image-upload
                  = f.fields_for :captured_images do |image|
                    %img
                    = image.file_field :content
                    = image.hidden_field :status, value: "sub"
      .row.proto-description
        .col-md-12
          %h4 Catch Copy
          = f.text_field :catch_copy, require: true, placeholder: "Input Catch Copy"
        .col-md-12
          %h4 Concept
          = f.text_area :concept, require: true, placeholder: "Input Concept"
      .row.text-center.proto-btn
        = f.submit "SAVE", id: "button", class: "btn btn-lg btn-primary btn-block"

prortotypes_controller.rb

class PrototypesController < ApplicationController
  before_action :set_prototype, only: [:show, :edit, :update]

  def index
    @prototypes = Prototype.all.page(params[:page]).per(10)
  end

  def new
    @prototype = Prototype.new
    @prototype.captured_images.new
  end

  def create
    @prototype = Prototype.new(prototype_params)
    if @prototype.save
      redirect_to :root, notice: 'New prototype was successfully created'
    else
      redirect_to ({ action: :new }), alert: 'New prototype was unsuccessfully created'
     end
  end

  def show
  end

  def edit
      @prototype.captured_images.find(params[:id])
  end

  def update
    if @prototype.update(prototype_params)
      redirect_to :root, notice: 'New prototype was successfully updated'
    else
      redirect_to ({ action: :new }), alert: 'New prototype was unsuccessfully updated'
    end
  end

  private

  def set_prototype
    @prototype = Prototype.find(params[:id])
  end

  def prototype_params
    params.require(:prototype).permit(
      :title,
      :catch_copy,
      :concept,
      :user_id,
      captured_images_attributes: [:id, :content, :status]
    )
  end
end