Negation of filterWhen and hasElement

Question

I'm learning Flux and Mono and am hitting a wall when trying to check if a key doesn't exist in redis. I need to filter my flux and want to remove the element if the key exists. I don't find a way to do this in the docs, all I can filter is to keep if the key exists. I need the opposite.

client.request(MWS_EU, Orders, ordersRequest, ListOrdersResponse.class)
    .flatMapIterable(listOrdersResponse -> listOrdersResponse.getOrders())
    .filterWhen(order -> isNewOrder(order.getOrderId()))
    .flatMap(...)

and the check for redis:

private Mono<Boolean> isNewOrder(String orderId) {
    return redisOrders.opsForValue().get(orderId).hasElement();
} 

What is a clean way to filter my Flux to keep elements only if the key does not exist?

I don't want to use block().

Answer 1

You can change your method to the following:

private Mono<Boolean> isNewOrder(String orderId) {
    return redisOrders.opsForValue().get(orderId).hasElement().map(b -> !b);
} 

By using the map() method you can just invert the value returned by hasElement().