Join 2 or more Firebase Observables

Question

i'am trying to build an Observable made of FirebaseObjectObservable, but first I have to query a Firebase list to get every key id for that FirebaseObjectObservable.

My data structure

players {
   player_1 {
      carsKeys: {
         car_id_1: true,
         car_id_2: true,
         car_id_3: true
         .....
      }
   },
   player_2 {
      ...
   }
}

cars {
   car_id_1 {
      property_1 : '123',
      property_2 : '456',
      ...
   },
   car_id_2 {
      ...
   }
   ...
}

I'am wishing to subscribe to just one Observable and to get an array of objects similar to this:

cars: Array[5]: [
                  {
                    id: car_id_1,
                    property_1 : '123',
                    property_2 : '456',
                    ...
                  },
                  {
                    id: car_id_2,
                    .....
                  },
                  ....
                 ]

My service function looks like this:

 public getCars(player_id){
    return this.db.list('players/' + player_id + '/carsKeys/')
           .map(carsKeys => carsKeys
                .map(key => this.db.object('cars/' + key)))
           .flatMap(carsObjs => Observable.combineLatest(carsObjs))
 }

I've tried a lot of combination but nothing works: I need that data structure and also I need to be synchronized with the database.

Answer 1

Let's see if I get your question correctly.

1. Get car keys from player selected player
2. Convert Car keys to an array for easy manipulation
3. Covert Car keys array to individual Observable stream
4. Get each car key details from cars table
5. Make it as car keys array

Here is code sample. Replace those query part with your firebase query https://jsbin.com/hokayilulu/edit?js,console,output

const players$ = Rx.Observable.of(players)
  .map(x => players[Object.keys(x).find(x=> x === 'player_1')])
  .map(x => Object.keys(x.carsKeys))
  .switchMap(x => Rx.Observable.from(x))
  .map(x => cars[x]);

let result = []
players$.subscribe(x => {
  result.push(x);
  console.log(result)
})