Combine firestore queries with rxjs (OR query)

Question

I'm trying to combine two firestore queries in an Ionic/Angular project using RxJS. I found this blog post from which explains the basic principle, however, the .combineLatest method has been deprecated and I can't figure out how to pipe the two queries into a map instead.

caOrCoCities$: Observable<City[]>;

...

const californiaRef = this.angularFirestore
    .collection("cities", ref => ref.where("state","==","CA"));
const coloradoRef = this.angularFirestore
    .collection("cities", ref => ref.where("state","==","CO"));

Not sure how to update this below...

this.caOrCoCities$ = Observable
    .combineLatest(californiaRef.valueChanges(),
                   coloradoRef.valueChanges())
    .switchMap(cities => {
        const [californiaCities, coloradoCities] = cities;
        const combined = californiaCities.concat(coloradoCities);
        return Observable.of(combined);
    });

What is the RxJS version you are using?

Nikhil
– Nikhil

2019-10-17 19:14:29 +00:00
Commented Oct 17, 2019 at 19:14 — Nikhil
– Nikhil, Commented Oct 17, 2019 at 19:14
@Nikhil version 6.4.0

Carrie M.
– Carrie M.

2019-10-17 19:26:17 +00:00
Commented Oct 17, 2019 at 19:26 — Carrie M.
– Carrie M., Commented Oct 17, 2019 at 19:26

Nikhil · Accepted Answer · 2019-10-17 19:29:01Z

4

RxJS 6 had several changes in syntax. You can change your code as shown below.

import { combineLatest, of } from 'rxjs';

this.caOrCoCities$ = combineLatest(californiaRef.valueChanges(), coloradoRef.valueChanges())
    .pipe(
       switchMap(cities => {
         const [californiaCities, coloradoCities] = cities;
         const combined = californiaCities.concat(coloradoCities);
         return of(combined);
       })
    );

answered Oct 17, 2019 at 19:29

Nikhil

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4 Comments

martin Over a year ago

The correct non-deprecated variant of combineLatest in RxJS 6 is the one that accepts arrays. combineLatest([a$, b$])

Nikhil Over a year ago

@martin - Looks like there are several overloads for this operator which are equally correct. I see both the variants in use in official docs, learn-rxjs, and in this migration guide.

martin Over a year ago

All these github.com/ReactiveX/rxjs/blob/master/src/internal/observable/… are deprecated

Nikhil Over a year ago

@martin - Thanks for the info. Looks like the docs aren't updated. I didn't see any mention of it anywhere.

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