Rxjs workflow for MongoDB Document References - mongodb

Question

I am developing an application on Ionic2/rc0. I got a ReplaySubject on a singlenton service that keeps the current user consistent across the whole app. It all works fine, I can subscribe to it and get a User object as easy as
this._user.Current.subscribe(user=>{ console.log(user)});
The User object looks like this
User {
confirmed:true
devices:["57f65werwe343bn8843f7h","7yr3243h5429hf2hjd"]
friends:["t245y53h65346htyh","356ytrer75dfhg43we56df"]
email:"francescoaferraro#gmail.com"
id:"57f6525e926bbc7615fc5c5c"
notification:false
password="$2a$04$.Fk/8eMj18ZrkfurbbdP4uT3yOs7Lb9db74GkNfgtABVY.ez2Q0I."
picture:"https://api.cescoferraro.xyz/kitty"
role:"master"
username:"cesco"
}
As you can see my backend is using MongoDB with One-to-Many Relationships with Document References as described here.
I have created a devices tab where I want to display all data about those user devices, but I need to call this._devices.info for each one of current.devices and concat the result back to TrueDevices
#Component({
template: `
<ion-header>
<ion-navbar>
<ion-title>Tabs</ion-title>
</ion-navbar>
</ion-header>
<ion-content>
<h2>Device:list</h2>
<h2 *ngFor="let item of devices | async">{{item}}</h2>
<button ion-button (click)="readDevice()">Read Random Device</button>
</ion-content>
`
})
export class DeviceComponent {
devices: Observable<string[]>;
TrueDevices: Observable<Device[]>;
constructor(public _user: UserService, public _device: DeviceService) {
this._user.Current.subscribe(user=>{ this.devices = Observable.of(user.devices)});
// Get current User
// call this._devices.info for each one of current.devices
// concat the result back to TrueDevices
this._user.Current
.subscribe((result) => { console.log(result) });
}
readDevice(){
console.log(this.devices);
this._device.info(this.devices.value[0]).subscribe(data=>console.log(data))
}
}
I will need to repeat the same procedure to the friends tab and so on. I am pretty sure there are a couple operators that would do the magic, but I am fairly new to rxjs and not familiar with all of them. Whats the right approach?

Answer 1

this._user.Current
.switchMap(user => Observable.from(user.devices)) // after this line, you have an Observable<string>
.mergeMap(device => this._device.info(device)) // each device will be mapped to another observable(or stream), and all the streams will be merged together
.toArray() // wait for all the streams to complete and reduce all the results into an array.
.subscribe(array => console.log(array));
or go to the gitter room:
https://gitter.im/Reactive-Extensions/RxJS