CODEWITHSUNDEEP
promiserxjs
user3743222
user3743222

Reputation: 18665

Convert a stream of Promises into a stream of values

I am somewhat new to RxJs and I am trying to mix the world of promises and observables.

Here is what I want: I have an observable (call it clickObs) which listens to a click and as a result interrogates a database, producing a promise which resolves to a value when the database querying concludes (successfully). My observable thus generates a stream of promises from a stream of clicks, and what I want is to generate from that observable, a stream of corresponding resolved values.

From past questions on stackoverflow, I read about defer, flatMap, mergeAll, and fromPromise, but cannot get my head around how to articulate the four to solve my problem.

Any suggestions?

Upvotes: 6

Views: 645

Answers (1)

paulpdaniels
paulpdaniels

Reputation: 18663

You shouldn't need all four, just look at flatMap or its sibling flatMapLatest

clickObs.flatMapLatest(function() {
  //Access the db and return a promis
  return database.query(queryObj);
})
.subscribe(function(result) {
  //Result is implicitly flattened out
  /*Do something with the result*/
});

flatMap will implicitly convert a promise or array-like object into an Observable and flatten out the resulting sequence. FlatMapLatest is similar but will ignore old events, if a newer one arrives before the previous one completed.

Upvotes: 4

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