Utilizing ngFor to iterate over items within an Observable array serving as unique identifiers

Just starting out with Angular and I'm really impressed with its power so far. I'm using the angularfire2 library to fetch two separate lists from firebase (*.ts):

this.list1= this.db.list("list1").valueChanges();
this.list2= this.db.list("list2").valueChanges();

As I iterate through the first list with *ngFor, I want to use list1.val as a key to access a value from list2

(list2[list1.val].name).

I've encountered various errors while experimenting with different approaches, but the most recurring one is:

TypeError: Cannot read property 'party' of undefined

This is how my *.html file looks right now (trying some async magic):

<ion-row *ngFor="let item1 of list1| async">
  <ion-col>{{item1.val}}</ion-col>
  <!--different attempts-->
  <ion-col>{{(list2|async)[item1.val].name}}</ion-col>
  <ion-col>{{(list2[item1.val].name| async)}}</ion-col>
  </ion-col>
</ion-row>

I suspect that ngFor may be altering the structure of list1 from:

Observable<any[]>

to an object that's easier to work with. Without that, it seems like my list2 object cannot be accessed without some kind of transformation. Any help would be appreciated :)

Answer №1

After seeking guidance from a helpful post, I managed to resolve this issue: Solving Nested Observables Rendering Problem in Angular2 with AngularFire2

The solution involved creating a map function to link an object observable to my second node:

this.list1= this.db.list("list1").snapshotChanges().map(changes => {
  return changes.map(list1Obj => ({
    l1Key: list1Obj.payload.key,
    list2Obj: this.db.object('list2/' + list1Obj.payload.key).valueChanges()
  }));
});

This allowed me to showcase the data in the HTML as follows:

  <ion-row *ngFor="let item1 of list1| async">
    <ion-col>{{item1.l1Key}}</ion-col>
    <ion-col>{{((item1.list2Obj | async)?.name)}}</ion-col>
  </ion-row>

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