Firebase data join with Observable - firebase

Question

Currently, I am stuck in a problem with Firebase Observable joins.
I do not really know which is the best way to get my data from different objects and join them together.
My data structure:
users {
userid1 {
conversationid: id
...
},
userid2 {
...
}
}
conversations {
conversationid {
...
}
}
Now I want to get all conversations of the current user.
To get the current user id I'll subscribe to the auth Observable like this:
this.af.auth.subscribe(auth => {
console.log(auth.uid);
});
As next I need the user's child object to get the conversation id. I'm doing that like this:
//needs the userid from Observable on top
this.af.database.object('/users/' + auth.uid)
.map(
user => {
console.log(user.conversationid);
}
)
.subscribe();
And the same for the conversations:
//needs the conversationid from the second Observable
this.af.database.list('/conversations/' + user.conversationid)
.subscribe();
As you can see, there are 3 Observables. I know it's possible to nest them, but in my project could this happen up to 5 times.
Is it possible to get the conversations without nesting 3 Observables?

Answer 1

You could do something like this:
let combined = this.af.auth
// Filter out unauthenticated states
.filter(Boolean)
// Switch to an observable that emits the user.
.switchMap((auth) => this.af.database.object('/users/' + auth.uid))
// Switch to an observable that emits the conversation and combine it
// with the user.
.switchMap((user) => this.af.database
.list('/conversations/' + user.conversationid)
.map((conversation) => ({ user, conversation }))
);
// The resultant observable will emit objects that have user and
// conversation properties.
combined.subscribe((value) => { console.log(value); });