500 error editing and updating multiple file uploads rails - ruby-on-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

The accepts_nested_attributes_for expects a hash for the *_attributes value that it processes, the hash it expects has the array indices as the keys, ie. it expects something like this:
asset_attributes: {
0 => { asset: value_for_0 },
1 => { asset: value_for_1 }
}
By creating the name of your form field as listing[assets_attributes][][asset] you're actually creating an array, ie.
asset_attributes: [
{ asset: value_for_0 },
{ asset: value_for_1 }
]
This is why you've received the error.
I think what you meant to name your field was: listing[assets_attributes][asset][] which would create:
asset_attributes: {
0 => { asset: [ array, of, IO, objects, for, your, files ] }
}

Answer 2

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.