AngularFirestore：检索集合中的文档引用并将 map 检索到 class

Question

I want to combine two firestore collections that are linked with an reference field.

I have these two collections:

I want to display the displayName of the referenced user with a single userstory instead of the id of an user.

Template:

<tbody id="project">
   <tr *ngFor="let userstory of userstories | async">
      <td>{{ userstory.name }}</td>
      <td>{{ userstory.description }}</td>
      <td>{{ userstory.status }}</td>  
      <td>{{ userstory.points }}</td>
      <td>{{ userstory.ownerobj.displayName }}</td> <!-- I want to display to displayName of the here -->
      <td>{{ userstory.uid }}</td>
   </tr>
</tbody>

Model:

export class Userstory {
  public uid: string;
  public name: string;
  public description: string;
  public status: number;
  public points: number;
  public owner: DocumentReference;
  public ownerobj: User;
}  

export class User {
  uid: string;
  email: string;
  displayName: string;
  photoURL: string;
  emailVerified: boolean;
}

Service:

getUserstories() {
return this.afs.collection<Userstory>('userstories')
  .snapshotChanges()
  .pipe(
    map(res => res.map(el => {
      let userstory = el.payload.doc.data() as Userstory;
      userstory.uid = el.payload.doc.id;
      this.afs.doc(`/users/${userstory.owner.id}`).snapshotChanges().pipe(map(item => {
        userstory.ownerobj = item.payload.data() as User
      }));
      return userstory;
    })),
  )
};

Obviusly the code above doesn't work because it is not an synchronous function. But how can I get this to work to combine the user with an userstory?

I'm trying to learn firestore but there isn't much information on how to do this. Any help is appreciated.

Answer 1

What I would recommend, is that you do not try to use a non-relational database as if it were a relational one, in the Owner property you must put all the necessary owner information.

If you don't want to work so then the most you can do is create a function that calls the owner's document and displays its data.

But in itself, a relatio is not posible.