Rails: Photo uploads (Paperclip) with nesting & strong params

Question

Background:

I'm trying to add photo uploads to an Advert model using Strong Params with the Paperclip gem, where Photo is a separate model which "has_attached_file" :upload, and I am calling forms_for (actually semantic_forms_for as I'm using Formtastic) in the Ads#new view to upload the image to the Photo instance. Params looks ok but I think I've missed something in the controller. Haven't been able to get it working despite multiple iterations of the controller code. What would I need to do differently to get it working?

Would appreciate any tips or pointers! Thank you

--

Ad model:

class Ad < ActiveRecord::Base
  belongs_to :user

    ##edited out irrelevant associations

  has_many :photos, dependent: :destroy
  accepts_nested_attributes_for :photos, :allow_destroy => true
  default_scope { order("created_at DESC") }
  #validates_presence_of :user_id, :make, :model, :km, :year, :location
end

--

Photo model:

 class Photo < ActiveRecord::Base
      belongs_to :ad
      has_attached_file :upload, :styles => { :main => "600x500>", 
                                                                                    :thumb => "60x45>" }, 
      :default_url => "http://placehold.it/600x500&text=nice+wheels!"
    end

AdsController

class AdsController < ApplicationController

    def create
        @ad = Ad.new(ad_params)
      @ad.user_id = current_user.id
      @photo = @ad.photos.build
        if @ad.save
            redirect_to @ad
        else
            flash.alert="You were missing some super-important details. Try again"
            redirect_to new_ad_path
        end
    end

    private

    def ad_params ##excluded all attributes except nested upload attrib. for gist
        params.require(:ad).permit(photos_attributes: [upload: [:upload_file_name, :upload_content_type]])
    end

end

Ads#new

 <%= semantic_form_for @ad do |form| %>

    <!-- left out all other form fields -->      

      <%= form.semantic_fields_for :photo do |photo| %>
        <%= photo.file_field :upload %>
      <% end %>

    <% end %>

Ad params hash after submit action (Ad#create)

{"location":"Abha","make":"Bentley","model":"","gear":"","km":"50","price_bid":"500","price_ask":"500","ac":"0","cd":"0","radio":"0","powersteering":"0","abs":"0","satnav":"0","cruise":"0","fwd":"0","convertible":"0","problem_1":"","problem_2":"","problem_3":"","description":"","photo":{"upload":{"original_filename":"mustang-290x218.jpg","content_type":"image/jpeg","headers":"Content-Disposition: form-data; name=\"ad[photo][upload]\"; filename=\"mustang-290x218.jpg\"\r\nContent-Type: image/jpeg\r\n","tempfile":[]}}}

Routes

resources :ads, only: [:new, :create, :show, :index, :edit, :destroy] do
        resources :comments, only: [:create, :destroy]
        resources :photos, only: [:create, :destroy]
        resources :favorite_ads, only: [:create, :destroy]
        resource :emails, only: :create 
  end

Answer 1

The form needs to be specified as multi-part for file uploads to work:

<%= semantic_form_for @ad, :html => {:multipart => true} do |form| %>

In addition, you aren't permitting the tempfile to be passed:

params.require(:ad).
       permit(photos_attributes: 
               [upload: 
                 [:upload_file_name, :upload_content_type, :tempfile]
               ])

Answer 2

params.require(:ad).permit(photos_attributes: :upload)

this should be enough.