firebase-admin.service.ts

// Use this instead of AngularfireDatabase in your ServerDatabaseService
import { Injectable, Inject, NgZone } from '@angular/core';
@Injectable()
export class FirebaseAdminService {
  constructor(
    @Inject('firebaseAdmin') private admin, // An initialized instance of firebase-admin, provided from the outside
    private zone: NgZone
  ) { }
  public snapshot(path, query): Promise<any> {
    let timeout = setTimeout(() => { // Give time for socket to return something before Universal exits.
      // Timeout gets canceled when the data's in, so this line won't be reached in a normal world.
    }, 10000);
    return new Promise<any>((resolve, reject) => {
      this.zone.runOutsideAngular(() => { // Out of Angular's zone so it doesn't wait for the neverending socket connection to end.
        let ref = this.applyQuery(this.admin.database().ref(path), query);
        ref.once('value').then(data => {
          this.zone.run(() => { // Back in Angular's zone
            resolve(data);
            setTimeout(() => { 
              // Maybe getting the data will result in more components to the view that need related data.
              // 20ms should be enough for those components to init and ask for more data.
              clearTimeout(timeout);
            }, 20);
          });
        }, err => reject(err));
      });
    });
  }
  private applyQuery(ref, query) {
    for (var n in query) {
      const val = query[n].getValue 
        ? query[n].getValue() // BehaviorSubject
        : query[n]; // Primitive
      switch (n) {
        case 'orderByKey':
          ref = ref.orderByKey();
          break;
        default:
          if (!(n in ref)) {
            break;
          }
          ref = ref[n](val);
          break;
      }
    }
    return ref;
  }
}