public function execute(Request $request)
 {
     $transactionsInPeriod = $this->transactions->getTransactionsInPeriod($request->getPeriodStart(), $request->getPeriodStart());
     $summaries = array_map(function ($transaction) {
         return new Summary($transaction[0], $transaction[1]);
     }, $transactionsInPeriod);
     return new Response(0, $summaries);
 }