Non-blocking functional methods with Reactive Mongo and Web client - mongodb

Question

I have a micro service which reads objects from a database using a ReactiveMongoRepository interface.
The goal is to take each one of those objects and push it to a AWS Lambda function (after converting it to a DTO). If the result of that lambda function is in the 200 range, mark the object as being a success otherwise ignore.
In the old days of a simple Mongo Repository and a RestTemplate this is would be a trivial task. However I'm trying to understand this Reactive deal, and avoid blocking.
Here is the code I've come up with, I know I'm blocking on the webClient, but how do I avoid that?
#Override
public Flux<Video> index() {
return videoRepository.findAllByIndexedIsFalse().flatMap(video -> {
final SearchDTO searchDTO = SearchDTO.builder()
.name(video.getName())
.canonicalPath(video.getCanonicalPath())
.objectID(video.getObjectID())
.userId(video.getUserId())
.build();
// Blocking call
final HttpStatus httpStatus = webClient.post()
.uri(URI.create(LAMBDA_ENDPOINT))
.body(BodyInserters.fromObject(searchDTO)).exchange()
.block()
.statusCode();
if (httpStatus.is2xxSuccessful()) {
video.setIndexed(true);
}
return videoRepository.save(video);
});
}
I'm calling the above from a scheduled task, and I don't really care about that actual result of the index() method, just what happens during.
#Scheduled(fixedDelay = 60000)
public void indexTask() {
indexService
.index()
.log()
.subscribe();
}
I've read a bunch of blog posts etc on the subject but they're all just simple CRUD operations without anything happening in the middle so don't really give me a full picture of how to implement these things.
Any help?

Answer 1

Your solution is actually quite close.
In those cases, you should try and decompose the reactive chain in steps and not hesitate to turn bits into independent methods for clarity.
#Override
public Flux<Video> index() {
Flux<Video> unindexedVideos = videoRepository.findAllByIndexedIsFalse();
return unindexedVideos.flatMap(video -> {
final SearchDTO searchDTO = SearchDTO.builder()
.name(video.getName())
.canonicalPath(video.getCanonicalPath())
.objectID(video.getObjectID())
.userId(video.getUserId())
.build();
Mono<ClientResponse> indexedResponse = webClient.post()
.uri(URI.create(LAMBDA_ENDPOINT))
.body(BodyInserters.fromObject(searchDTO)).exchange()
.filter(res -> res.statusCode().is2xxSuccessful());
return indexedResponse.flatMap(response -> {
video.setIndexed(true);
return videoRepository.save(video);
});
});

Answer 2

my approach, maybe a little bit more readable. But I admit I didn't run it so not 100% guarantee that it will work.
public Flux<Video> index() {
return videoRepository.findAll()
.flatMap(this::callLambda)
.flatMap(videoRepository::save);
}
private Mono<Video> callLambda(final Video video) {
SearchDTO searchDTO = new SearchDTO(video);
return webClient.post()
.uri(URI.create(LAMBDA_ENDPOINT))
.body(BodyInserters.fromObject(searchDTO))
.exchange()
.map(ClientResponse::statusCode)
.filter(HttpStatus::is2xxSuccessful)
.map(t -> {
video.setIndexed(true);
return video;
});
}