使用angular查询来自firestore的动态输入的实时数据

到目前为止，我已经尝试了这个，我能够获取所有数据，但我只想要与用户选择的输入相对应的数据。我是新手，有任何建议。

component.html： -

Name: <select [(ngModel)] = "selectedLevel" (change)="selected()"> <option *ngFor="let post of posts | async" [ngValue]="post">{{post.user}}

Component.ts： -

export interface Post{ user: string; callType : string; callDuration: string; callTime : string; }

@Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css'] })

export class AppComponent { constructor (private afs:AngularFirestore){ } public CallDetails: object = []; public calls =[];

postsCol: AngularFirestoreCollection posts: Observable<Post[]>

selectedLevel; ngOnInit(){

this.postsCol = this.afs.collection<Post>('acb', ref => ref.orderBy('user', 'asc'));
this.posts = this.postsCol.snapshotChanges().map(actions => {
  return actions.map(a => {
    const data = a.payload.doc.data() as Post;
    const id = a.payload.doc.id;
    return { id, ...data };
  })
})
 return this.posts;

}

这是我想要的输出格式