Rails 4 Unknown format after upload image

Question

I have a submit form (I'm using simple form) in a bootstrap modal that submits some data and a image, when I don't submit the image (I leave it blank) the form submits the data without problem but when I submit the image it says:

ActionController::UnknownFormat

Form:

<%= simple_form_for resource, remote: true do |f| %>
  <%= token_tag form_authenticity_token %>
  <%= f.input :design_board_id, as: :hidden %>
  <%= f.input :style, collection: ["Playera", "Blusa", "Short"], prompt: "Selecciona un tipo" %>
  <%= f.input :model %>
  <%= f.input :cost %>
  <%= f.input :description %>
  <%= f.input :image %>
  <%= f.association :production_sequence, prompt: true %>
  <%= f.button :submit, class: "btn-success" %>
<% end %>

Controller:

def create
  @models_definition = ModelsDefinition.new(params.require(:models_definition).permit(permitted_attributes))
  if @models_definition.save
    redirect_to models_definitions_path
  else
    respond_to do |format|
      format.js { render "create" }
    end
  end
end

The error is in this line:

respond_to do |format|

Model:

class ModelsDefinition < ActiveRecord::Base

  belongs_to :production_sequence
  has_many :serigraphies, dependent: :destroy
  has_many :technique_selectors, dependent: :destroy
  belongs_to :accoutrement
  belongs_to :design_board

  mount_uploader :image, ImageUploader

  validates :style, :model, :cost, :production_sequence_id, presence: true

  accepts_nested_attributes_for :technique_selectors, reject_if: :all_blank
  accepts_nested_attributes_for :serigraphies, reject_if: :all_blank

end

Answer 1

You need to tell your form that you'll be uploading binary data, hence you have to make it a multipart form:

<%= simple_form_for resource, html: {multipart: true}, remote: true do |f| %>