AngularFire - 如何将 firestore 文档映射到 valueChanges 上的数组？

Question

In my angular web app I'm using the angularfire library to interact with firestore.

In the constructor of a component I would like to subscribe to a collection of documents and map the docs to an array when the value changes function is triggered.

I can easily display the list in the front end using the provided syntax.

//component constructor
constructor(private afs: AngularFirestore) {
    this.itemsCollection = afs.collection<Item>('items');
    this.items = this.itemsCollection.valueChanges();
  }


//component template
<ul>
  <li *ngFor="let item of items | async">
    {{ item.name }}
  </li>
</ul>

However, I need an array (or object) of the documents in that collection because I need to do some logic to render other things. For example I have a "isChecked" function that decides if a checkbox is checked based on if an item exists in that collection of documents.

async isChecked(itemID) {
    if(items[itemID]) {
     return true;
     } else {
     return false 
     }
}

So, how can I get the documents to another variable and keep it updated on valueChanges?

Answer 1

this.itemsCollection.valueChanges()
.pipe(
  tap(res => {
   this.items = res;
  })
)
.subscribe();

and after this need to remove the async pipe from html, in this case u will be able to use items as object or array, not as observable, maybe it will be easier for you. Also don't forget to unsubscribe in ngOnDestroy

Answer 2

你可以使用 rxjs 地图操作符

this.items = this.itemsCollection.valueChanges().pipe(map (res) => ... );