Rails in Action - 私有化资产

Question

管理员登录并创建了与项目相关的故障单，然后正确上传了附件，没有任何错误，然后当我尝试下载时，它变为错误状态，当我用can?替换cannot?时能够下载资产，那么在不改变当前控制器显示动作的情况下，管理员能够下载它需要什么？

注意：如果用户没有权限查看资产，应该会出现错误情况，但我不知道管理员如何发生这种情况也无法在书中找到它。有没有人经历过这个？

class FilesController < ApplicationController
    before_filter :authenticate_user!

    def show
        asset = Asset.find(params[:id])
        if  can?(:view, asset.ticket.project)
            send_file asset.asset.path, :filename => asset.asset_file_name,
                                        :content_type => asset.asset_content_type
        else
            flash[:alert] = "The asset you were looking for could not be found."
            redirect_to root_path
        end
    end
end

Ability.rb

class Ability
    include CanCan::Ability

    def initialize(user)
        user.permissions.each do |permission|
            can permission.action.to_sym, permission.thing_type.constantize do |thing|
                thing.nil? || permission.thing_id.nil? || permission.thing_id == thing.id
            end
        end
    end
end