如何用AngularFire查询实时数据库？

npm install firebase @angular/fire

export const environment = {
  production: false,
  firebaseConfig: {
    apiKey: "<YOUR_API_KEY>",
    authDomain: "<YOUR_AUTH_DOMAIN>",
    databaseURL: "<YOUR_DATABASE_URL>",
    projectId: "<YOUR_PROJECT_ID>",
    storageBucket: "<YOUR_STORAGE_BUCKET>",
    messagingSenderId: "<YOUR_MESSAGING_SENDER_ID>",
    appId: "<YOUR_APP_ID>",
  },
};

import { AngularFireModule } from '@angular/fire';
import { environment } from '../environments/environment';

@NgModule({
  imports: [
    AngularFireModule.initializeApp(environment.firebaseConfig),
    // 其他模块导入
  ],
  // ...
})
export class AppModule { }

import { AngularFireDatabase } from '@angular/fire/database';

constructor(private db: AngularFireDatabase) { }

items: Observable<any[]>;

ngOnInit() {
  this.items = this.db.list('items').valueChanges();
}

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