code: public function findByCustomer(CustomerInterface $customer, $limit = null)
      {
          $qb = $this->createQueryBuilder('i');
  
          $qb
              ->join('i.order', 'o')
              ->andWhere($qb->expr()->eq('o.customer', ':customer'))
              ->andWhere($qb->expr()->eq('o.sample', ':sample'))
              ->addOrderBy('i.createdAt', 'ASC');
  
          if (0 < $limit) {
              $qb->setMaxResults($limit);
          }
  
          return $qb
              ->getQuery()
              ->setParameter('customer', $customer)
              ->setParameter('sample', false)
              ->getResult();
      }
docs: @inheritdoc
  
  @return OrderInvoiceInterface[]