my proplisting code updates

firebase.service.ts

import { Injectable } from '@angular/core';
import { AngularFireModule } from 'angularfire2';
import { AngularFireDatabaseModule } from 'angularfire2/database';
import { AngularFireDatabase, FirebaseListObservable } from 'angularfire2/database';
import 'rxjs/add/operator/do';

@Injectable()
export class FirebaseService {
      listings: FirebaseListObservable<any[]>;
      // now this is called as a stand alone constructor
      constructor(private af: AngularFireDatabase) {}
      // the get method is called outside the custrustor now in the latest Angular2 version and we use the created instance
      // of the af object
        getListings(){
          this.listings = this.af.list('/listings') as FirebaseListObservable<listing[]>;
          return this.listings;
        }
      }

interface listing {
  $key?:string;
  title?:string;
  title_ar?:string;
  type?:string;
  city?:string;
  city_ar?:string;
  image?:string;
  owner?:string;
  owner_ar?:string;
  bedrooms?:string;
}