Flatten/Chain multiple nested firebase Observables - firebase

Question

I'm trying to use AngularFire2. I am querying and everything works fine below.
I want to combine all/most of the observables into one:
getTournamentWithRounds(key):Observable<Tournament> {
return this.af.database
.object(`/tournaments/${key}`)
.map(tourney => {
let t = Tournament.fromJson(tourney);
this.af.database.list('players', {
query: {
orderByChild: 'tournament_key',
equalTo: key
}
})
.map(Player.fromJsonList)
.subscribe(ps => { t.players = ps; });
this.af.database.list('rounds', {
query: {
orderByChild: 'tournament_key',
equalTo: key
}
})
.map(Round.fromJsonList)
.subscribe(rs => { t.rounds= rs; })
return t;
})
}
I was wondering if I could join all the observables and get the output with a single subscribe function.
I would like to know when all the initial data has been loaded and perform additional computation in the controller before outputting it to the view.
Also, how could this be extended to include the matches for each round?
My extension to the above code would be:
...
this.af.database.list('rounds', {
query: {
orderByChild: 'tournament_key',
equalTo: key
}
})
.map(rounds => {
return rounds.map((round) => {
let r = Round.fromJson(round);
this.af.database.list('matches', {
query: {
orderByChild: 'round_key',
equalTo: round.$key
}
})
.map(Match.fromJsonList)
.subscribe(matches => { r.matches = matches; })
return r;
})
})
.subscribe(rs => { t.rounds= rs; })
...

Answer 1

You could use the combineLatest operator to combine the players and rounds with the tournament:
getTournamentWithRounds(key): Observable<Tournament> {
return this.af.database
.object(`/tournaments/${key}`)
.combineLatest(
this.af.database.list('players', {
query: {
orderByChild:'tournament_key',
equalTo: key
}
}),
this.af.database.list('rounds', {
query: {
orderByChild:'tournament_key',
equalTo: key
}
})
)
.map(([tourney, players, rounds]) => {
let t = Tournament.fromJson(tourney);
t.players = Player.fromJsonList(players);
t.rounds = Round.fromJsonList(rounds);
return t;
});
}
Whenever any of the observables emits, the latest values will be re-combined and a new Tournament will be emitted.
Extending this to include each round's matches is a little more complicated, as each round's key is needed for the matches query.
The emitted rounds can be mapped to an array of list observables for the matches and forkJoin can be used to join the observables, with the forkJoin selector function being used to combine the matches with the rounds. switchMap is then used to emit the rounds.
getTournamentWithRounds(key): Observable<Tournament> {
return this.af.database
.object(`/tournaments/${key}`)
.combineLatest(
this.af.database.list('players', {
query: {
orderByChild:'tournament_key',
equalTo: key
}
}),
this.af.database.list('rounds', {
query: {
orderByChild:'tournament_key',
equalTo: key
}
})
.switchMap(rounds => {
Observable.forkJoin(
rounds.map(round => this.af.database.list('matches', {
query: {
orderByChild: 'round_key',
equalTo: round.$key
}
}).first()),
(...lists) => rounds.map((round, index) => {
let r = Round.fromJson(round);
r.matches = Match.fromJsonList(lists[index]);
return r;
})
)
})
)
.map(([tourney, players, rounds]) => {
let t = Tournament.fromJson(tourney);
t.players = Player.fromJsonList(players);
t.rounds = rounds;
return t;
});
}