/**
  * Register the failed job services.
  *
  * @return void
  */
 protected function registerFailedJobServices()
 {
     // Add compatible queue failer if mongodb is configured.
     if (config('queue.failed.database') == 'mongodb') {
         $this->app->singleton('queue.failer', function ($app) {
             return new MongoFailedJobProvider($app['db'], config('queue.failed.database'), config('queue.failed.table'));
         });
     } else {
         parent::registerFailedJobServices();
     }
 }