AddOrder.java

// r2dbc
public Mono<OrderDTO> addOrder(@RequestParam("bookIsbn") String bookIsbn, @RequestParam("firstName") String firstName) {
    return Mono.just(UUID.randomUUID()).flatMap(uuid -> {
        log.info("addOrder() {} running", uuid);

        Mono<User> user = userRepository.findByFirstName(firstName);
        Mono<Book> book = bookRepository.findByIsbn(bookIsbn);

        return Mono.zip(user, book).flatMap(zipFlux -> {
                    log.info("addOrder() {} I've got user and book", uuid);
                    Order order = new Order();
                    order.setUserId(zipFlux.getT1().getUserId());
                    order.setBookId(zipFlux.getT2().getBookId());
                    order.setQuantity(1);
                    return orderRepository.save(order).map(orderMapper::toDto);
                }
        ).doFinally((s) -> {
            log.info("addOrder() {} executed", uuid);
        });
    });
}

// jdbc
public ResponseEntity<OrderDTO> addOrder(@RequestParam("bookIsbn") String bookIsbn, @RequestParam("firstName") String firstName) {
    UUID uuid = UUID.randomUUID();
    log.info("addOrder() {} running", uuid);

    User user = userRepository.findByFirstName(firstName);
    Book book = bookRepository.findByIsbn(bookIsbn);
    log.info("addOrder() {} I've got user and book", uuid);

    Order order = new Order();
    order.setUser(user);
    order.setQuantity(1);
    order.setBook(book);
    order = orderRepository.save(order);

    OrderDTO orderDTO = orderMapper.toDto(order);
    log.info("addOrder() {} executed", uuid);
    return ResponseEntity.ok(orderDTO);

}

Code snippet Related to medium article:

https://blog.devgenius.io/an-epic-tale-comparing-jdbc-and-r2dbc-in-a-real-world-scenario-part-2-2-d908df49651c#823f-8a39553a5cf4