android - Chaining requests in Retrofit + RxJava

Question

I have 2 APIs that I want to make request to in sequence and store their data in SQLite.

First I want to make request to API A and store its data in SQL table a. Then make request to API B and store its data in table b and some data in table a_b. The data stored in a_b is from request B alone.

How can I do this using RxJava. I read somewhere about using flatMap for this, something like this

apiService.A()
    // store in DB here? How? maybe use map()?
    .flatMap(modelA -> {
        // or maybe store modelA in DB here?
        return apiService.B().map(modelB -> {
            storeInDB()l // store B here ?
            return modelB;
        });
    });

If I wasn't using lambda functions, this would look as ugly as normal nested calls. Is this a better way to do it?

Answer 1

I don't think using map operator is the best way to go with things like storing the result of the api call.

What I like to do is to separate those things inside doOnNext operators. So your example would be something like this:

apiService.A()
        .doOnNext(modelA -> db.store(modelA))
        .flatMap(modelA -> apiService.B())
        .doOnNext(modelB -> db.store(modelB));

(add necessary observeOn and subscribeOn yourself, exactly like you need them)