在 Spring Data Mongodb Reactive 中执行顺序查询

Question

I have to found All documents in collection B not referenced in collection A.

Using the method in ReactiveMongoRepository

Flux<A> findAll();

So I made this code:

collectionARepository.findAll()
    .flatMap(d -> d.documentBID())
    .collectList()
    .flatMap(list -> collectionBRepository.findDocsNotIn(list))
    .flatMap(b -> log.info(b.id())
    .subscribe();

But, if there's no documents in collection A, the second query will not be executed. How can I force the execution of second to get all documents.

Answer 1

Found the solution.

My IDE for some reason was not show error, but When I use collectList I passed from Flux to Mono. When I call flatMap (It should show an error) I cannot return a Flux, only a Mono. That causes an Exception and It was treat like "Entity not found". My bad.

So here is my final code:

collectionARepository.findAll()
    .flatMap(d -> d.documentBID())
    .collectList()
    .flatMapMany(list -> collectionBRepository.findDocsNotIn(list))
    .flatMap(b -> log.info(b.id())
    .subscribe();