Reactor spring mongodb repository combine multiple results together

Question

I'm kind of new to reactive programing and currently working on a spring webflux based application. I'm stuck between few questions.

public class FooServiceImpl {

@Autowired
private FooDao fooDao;

@Autowired
private AService aService;

@Autowired
private BService bService;

public long calculateSomething(long fooId) {
    Foo foo = fooDao.findById(fooId); // Blocking call one

    if (foo == null) {
        foo = new Foo();
    }

    Long bCount = bService.getCountBByFooId(fooId); // Blocking call two
    AEntity aEntity = aService.getAByFooId(fooId);  // Blocking call three

    // Do some calculation using foo, bCount and aEntity
    // ...
    // ...

    return someResult;
}
}

This is the way we write a blocking code which uses three external API call results (let's consider as DB calls). I'm struggling to convert this into a reactive code, If all three becomes mono and if I subscribe all three will the outer subscriber get blocked?

public Mono<Long> calculateSomething(long fooId) {
    return Mono.create(sink -> {
        Mono<Foo> monoFoo = fooDao.findById(fooId); // Reactive call one
        monoFoo.subscribe(foo -> {
            if (foo == null) {
                foo = new Foo();
            }

            Mono<Long> monoCount = bService.getCountBByFooId(fooId);  // Reactive call two

            monoCount.subscribe(aLong -> {
                Mono<AEntity> monoA = aService.getAByFooId(fooId);  // Reactive call three
                monoA.subscribe(aEntity -> {
                    //...
                    //...
                    sink.success(someResult);
                });
            });
        });
    };
  }

I saw there is a function called zip, but it only works with two results, So is there a way to apply it here?

Also what will happen if we get subscribe for something inside create method, Will it block the thread?

Would be very thankful if you could help me.

Answer 1

If you gave me the calculation you want you do with those values, it would be easier for me to show the reactor way of doing it. But lets suppose you want to read a value from database and then use that value for another thing. Use flatmaps and make a unique Flux reducing the lines of code and complexity, no need to use subscribe() as told by the other people. Example:

return fooDao.findById(fooId)
.flatmap(foo -> bService.getCountBByFooId(foo))
.flatmap(bCount -> aService.getAByFooId(fooId).getCount()+bCount);