如何在Firestore上获取集合的每个文档的一个字段？

Question

I'm trying to get just one field of every document of one collection. What i'm doing is to do a subscribe method to fill a list for a dynamic filter, but i know it doesnt work, what is the best way to get just what i want? I would like to be subscribed to it, here is my code:

this.af.collection('objects').valueChanges().subscribe(data => {        
  this.listTitles.push(data.title)
});

Answer 1

.subscribe won't work in your case, probably you need to split your code like this,

this.objectCollectionRef = this.af.collection('objects');
this.objectCollection = this.objectCollectionRef.valueChanges();


for(let data of this.objectCollection){
   this.listTitles.push(data.title)
}

Hope this helps!

Answer 2

Just map the result and use async in your template

class YourComponent{
  listTitles:Observable<String>;

  constructor(){
    this.listTitles = this.af.collection('objects').valueChanges().pipe(
      map(objs => objs.map(obj => obj.title))
    )
  }
}

And in your template :

<ng-container *ngFor="let item of listTitles | async">
 <!-- have fun -->
</ng-container>