code: @Override
      public ReservedDBInstance purchaseReservedDBInstancesOffering(PurchaseReservedDBInstancesOfferingRequest request) {
          request = beforeClientExecution(request);
          return executePurchaseReservedDBInstancesOffering(request);
      }
docs: <p>
  Purchases a reserved DB instance offering.
  </p>
  
  @param purchaseReservedDBInstancesOfferingRequest
  @return Result of the PurchaseReservedDBInstancesOffering operation returned by the service.
  @throws ReservedDBInstancesOfferingNotFoundException
  Specified offering does not exist.
  @throws ReservedDBInstanceAlreadyExistsException
  User already has a reservation with the given identifier.
  @throws ReservedDBInstanceQuotaExceededException
  Request would exceed the user's DB Instance quota.
  @sample AmazonRDS.PurchaseReservedDBInstancesOffering
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/rds-2014-10-31/PurchaseReservedDBInstancesOffering"
  target="_top">AWS API Documentation</a>