RxJava Emit initial value from downstream observable from flatmap

Question

I have a use case where I have to convert a button press to database fetch. I have an Observable from the button press. I am doing a flatMap of the observable to another observable which fetches items from the DB.

Observable<Customer> customerListObservable = getButtonPressObservable()
        .map(event -> new Object())
        .startWith(new Object())
        .flatMap(event -> DatabaseHelper.getDatabase()
                .select("select * from Customer")
                .autoMap(Customer.class)
                .toObservable());

However before button being pressed, I would need to fetch items from db for the first time. Again, on subsequent button presses, fetches should happen again.

Is there any other clean way other than the above code to generate initial value?

score 0 · Answer 1 · answered Aug 08 '18 at 07:24

0

I would concat the observables:

Observable<Customer> customerObservable = Observable.concat(getFromDb(), getAfterClick());

private Observable<Customer> getFromDb() {
   return DatabaseHelper.getDatabase()
                .select("select * from Customer")
                .autoMap(Customer.class)
                .toObservable());
}

private Observable<Customer> getAfterClick() {
   return getButtonPressObservable()
        .map(event -> new Object())
        .startWith(new Object())
        .flatMap(event -> getFromDb());
}

answered Aug 08 '18 at 07:24

Tatu Lahtela

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Thanks for the suggestion Tatu. Is there any advantage of using concat over startWith? – prem Aug 08 '18 at 07:45
No it is effectively be the same and is a matter of preference. In fact startWith just calls concat. – Tatu Lahtela Aug 08 '18 at 12:03

RxJava Emit initial value from downstream observable from flatmap

1 Answers1