Fixed controller to resolve problem with dragonfly caching

gistfile1.rb

class Admin::SermonsController < ApplicationController

  expose(:sermons) { policy_scope(Sermon) }
  expose :sermon, attributes: :sermon_params, finder: :find_by_url
  expose(:paginated_sermons) { sermons.page(params[:page]) }

  before_action :authorize_sermon, except: :index

  def index
    authorize(sermons)
  end

  def new;end

  def create
    if sermon.save
      flash[:success] = 'Sermon successfully uploaded.'
      redirect_to [:admin, sermon]
    else
      render action: 'new'
    end
  end

  def show;end

  def edit;end

  def update
    if sermon.save
      flash[:success] = 'Sermon successfully updated.'
      redirect_to admin_sermons_path
    else
      render action: 'edit'
    end
  end

  def destroy
    sermon.destroy
    flash[:success] = 'Sermon deleted.'
    redirect_to admin_sermons_path
  end

  private
  def sermon_params
    # This is the key line - both :image and :retained_image were missing,
    # so the image attribute wasn't going to work full stop.
    params.require(:sermon).permit(:title, :preacher, :date, :summary, :audio,
      :audio_cache, :image, :retained_image, :passage, :keywords)
  end

  def authorize_sermon
    authorize(sermon)
  end

end