500 error editing and updating multiple file uploads rails

Question

I'm using Paperclip and I've added multiple file uploads to one of my models. Everything works fine except when I try to add new files to the existing ones already uploaded. It throws this error:

Unexpected error while processing request: expected Hash (got Array) for param `assets_attributes'

How can I fix this so that I can add new files? Thanks in advance.

asset.rb

class Asset < ActiveRecord::Base

  belongs_to :member
  belongs_to :listing

  attr_accessible :asset

  has_attached_file :asset, styles: { large: "700x700>", thumb: "100x100#" }

  validates_attachment_size :asset, :less_than_or_equal_to=>10.megabyte
  validates_attachment_content_type :asset, :content_type=>['image/jpeg', 'image/jpg', 'image/png', 'image/gif']

end

listing.rb

has_many :assets, :dependent => :destroy
accepts_nested_attributes_for :assets, :allow_destroy => true

attr_accessible :assets_attributes

listings/_edit_form.html.erb

<%= simple_form_for(@listing, :html => { class: 'form-horizontal ', :multipart => true }) do |f| %>
  <% if @listing.errors.any? %>
    <%= f.error_notification %>

    <div>
        <%= file_field_tag('listing_assets_asset', multiple: true, name: "listing[assets_attributes][][asset]", id: 'file-upload3', class: '') %>
    </div>

<% end %>

listings_controller.rb

  before_filter :authenticate_member!, only: [:new, :create, :edit, :update, :destroy] 
  before_filter :find_member
  before_filter :find_listing, only: [:edit, :update, :destroy]

  def new
    @listing = Listing.new

    respond_to do |format|
      format.html # new.html.erb
      format.json { render json: @listing }
    end
  end

  # GET /listings/1/edit
  def edit

  end

  # POST /listings
  # POST /listings.json
  def create
    @listing = current_member.listings.new(params[:listing])

    respond_to do |format|
      if @listing.save
        current_member.create_activity(@listing, 'created')
        format.html { redirect_to @listing }
        format.json { render json: @listing, status: :created, location: @listing }
      else
        format.html { render action: "new" }
        format.json { render json: @listing.errors, status: :unprocessable_entity }
      end
    end
  end

  # PUT /listings/1
  # PUT /listings/1.json
  def update

    respond_to do |format|
      if @listing.update_attributes(params[:listing])
        format.html { redirect_to @listing }
        format.json { head :no_content }
      else
        format.html { render action: "edit" }
        format.json { render json: @listing.errors, status: :unprocessable_entity }
      end
    end
  end

  private

    def find_member
      @member = Member.find_by_user_name(params[:user_name])
    end 

    def find_listing
      @listing = current_member.listings.find(params[:id])
    end

Answer 1

That fixed the error issue but did not fix my overall problem. I found the fix to my problem by looking at this article: http://www.railscook.com/recipes/multiple-files-upload-with-nested-resource-using-paperclip-in-rails/

I needed to change the way I was handling multiple uploads.

Changing my input to this:

<%= file_field_tag "assets[]", type: :file, multiple: true, id: 'file-upload3' %>

and adding the following to my create and update actions in my controler:

if params[:assets]
    params[:assets].each { |asset|
      @listing.assets.create(asset: asset)
    }
end

Doing these things resolved my issue.