Go from Array of FirebaseListObservables to Array of Strings

Question

EDITED TO INCLUDE MORE DETAIL:

Let's assume I have a collection of Survey objects in Firebase, and a collection of SurveyTaker objects in Firebase, and a surveyTakersBySurvey relationship setup like

+-- surveyTakersBySurvey
   |
   +-- survey1
   |    |
   |    +-- surveyTaker1 = true
   |
   +-- survey2
        |
        +-- surveyTaker1 = true

This code currently works

findSurveyByState(surveyState:string): Observable<Survey> {
    return this.db.list('surveys', {
        query: {
            orderByChild: 'state',
            limitToFirst: 1,
            equalTo: surveyState
        }
    })
    .map(results => results[0]);
}

findSurveyTakerKeysPerSurveyState(surveyState:string,
                           query: FirebaseListFactoryOpts = {}): Observable<string[]> {
    return this.findSurveyByState(surveyState)
        .do(val => console.log("survey",val))
        .filter(survey => !!survey)
        .switchMap(survey => this.db.list(`surveyTakersBySurvey/${survey.$key}`,query))
        .map( stsbs => stsbs.map(stbs => stbs.$key) );
}

I need to change the above code to work for multiple surveys returned with the same state.

I'm struggling with rxjs programming...

//i first changed this to return multiple
findSurveysByState(surveyState:string): Observable<Survey[]> {
    return this.db.list('surveys', {
        query: {
            orderByChild: 'state',
            equalTo: surveyState
        }
    })
    //.map(results => results[0]);
}

// this is the method that is not working
findSurveyTakerKeysPerSurveyState(surveyState:string,
                           query: FirebaseListFactoryOpts = {}): Observable<string[]> {
    //need to update to take multiple Surveys
    return this.findSurveysByState(surveyState)
        .do(val => console.log("surveys",val))
        .filter(survey => !!survey)
        //.switchMap(survey => this.db.list(`surveyTakersBySurvey/${survey.$key}`,query))
        // switchMap would only make sense for one at a time?
        .map(surveys => surveys.map(survey => this.db.list(`surveyTakersBySurvey/${survey.$key}`, query)))
        // on the below line i get [ts] Property '$key' does not exist on type 'FirebaseListObservable<any[]>'.
        .map( stsbs => stsbs.map(stbs => stbs.$key) );
}

I get an [undefined, undefined]

Any help would be appreciated. Let me know if i need to elaborate on anything important.. i'm still feeling my way around here.

EDIT: this.db is from ... import { AngularFireDatabase } from "angularfire2/database";

when you console.log('stbss'), does it already contains the .$key in each of the element of the array? — CozyAzure
– CozyAzure, Commented Dec 18, 2017 at 5:41
It prints array of two FirebaseListObservables ... [FirebaseListObservable, FirebaseListObservable] ... i'm not sure how to print them out. — Kirby
– Kirby, Commented Dec 18, 2017 at 5:44
if you are using chrome console, you should be able to expand and see the objects inside — CozyAzure
– CozyAzure, Commented Dec 18, 2017 at 5:50
Yea it's a big crazy object like . 0 : FirebaseListObservable $ref : U {u: Qg, path: E, m: lf, Nc: false, then: undefined, …} operator : ObserveOnOperator {scheduler: ZoneScheduler, delay: 0} source : FirebaseListObservable {_isScalar: false, _subscribe: ƒ, $ref: U} _isScalar : false proto : Observable — Kirby
– Kirby, Commented Dec 18, 2017 at 5:54
it appears to be the same objects as a this.db.list('foo', query) . .. i'm just not sure how to map those to an array of strings — Kirby
– Kirby, Commented Dec 18, 2017 at 5:55

coturiv · Accepted Answer · 2017-12-18 17:00:07Z

2

Use combineLatest.

findSurveyTakerKeysPerSurveyState(surveyState:string,
    query: FirebaseListFactoryOpts = {}): Observable<string[]> {
  //need to update to take multiple Surveys
  return this.findSurveysByState(surveyState)
  .do(val => console.log("surveys",val))
  .filter(survey => !!survey)
  //.switchMap(survey => this.db.list(`surveyTakersBySurvey/${survey.$key}`,query))
  // switchMap would only make sense for one at a time?
  .switchMap(surveys => {
    let observables = [];
    surveys.forEach(survey => {
      observables.push(this.db.list(`surveyTakersBySurvey/${survey.$key}`, query));
    });
    return Observable.combineLatest(observables);
  })
  .map( stsbs => stsbs.map(stbs => stbs.$key) );
}

You may need to import these two lines.

import 'rxjs/add/observable/combineLatest';
import { Observable } from 'rxjs/Observable';

answered Dec 18, 2017 at 17:00

coturiv

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2 Comments

Kirby Over a year ago

Well, you are just amazing. Thank you. I also needed to add .map( stsbs => stsbs.map(results => results[0]).map(stbs => stbs.$key) );

coturiv Over a year ago

Glad to hear that.

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