DB::raw('SELECT w.id as w_id, w.first_name as first_name, SUM(worktime) as summary FROM workers as w LEFT JOIN work_times as wt ON wt.worker_id=w.id GROUP BY w_id, first_name');

public function workTimes()
{
  return $this->hasMany(WorkTime::class);
}

$workers = Worker::get();

$workers->each(function (Worker $worker) {
    $worker->workTimes()->sum('worktime');
});

$workers= Worker::with('workTimes')->get();

$workers->each(function (Worker $worker) {
  $worker->workTimes->sum('worktime');
});