Firebase - 检索单个对象

Question

对不起，长期以来的问题。我有一个事件列表，我得到这样的：

export class HomePageComponent implements OnInit { 

    events: FirebaseListObservable<EventModel[]>; 

    constructor(
    private authService: AuthService, 
    private router: Router, 
    private db: AngularFireDatabase 
) { 
    this.events = db.list('/events'); 
    } 

    ngOnInit() { 
    } 

} 

事件显示是这样的：

<md-card *ngFor="let event of events | async"> 
    <a [routerLink]="['event', event.slug]"><img class="event-img" src="http://lorempixel.com/30/30" />{{ event.name }}</a> 
</md-card> 

的event.component看起来是这样的：

export class EventComponent implements OnInit { 

    event: Object; 
    name: String; 

    constructor(db: AngularFireDatabase, route: Router) { 

    const eventQuery = db.list('/events', { 
     query: { 
     orderByChild: 'slug', 
     equalTo: 'event-name' 
     } 
    }).subscribe(data => { 
     this.event = data[0]; 
    }); 

    } 

    ngOnInit() { 
    } 

} 

this.event完成，正在查询正确的信息。它看起来像这样：

Object {category: "category", description: "description", googleMap: "map", guests: Object, name: "Event name"…} 
category: "category" 
description: "description" 
googleMap: "map" 
guests: Object 
name: "Event name" 
slug: "event-name" 
venue: "The venue" 
$exists: function() 
$key: "-xxxxxxxx" 
__proto__: Object 

当我试图展示我得到一个错误的名字{{event.name}}

ERROR TypeError: Cannot read property 'name' of undefined 
at Object.eval [as updateRenderer] 

其他问题：

由于该事件的信息已经在HomePageComponent存在，可以说，它是发送到EventComponent并用于显示事件？也许这会避免额外的数据库查询。

Answer 1

使用安全操作?

<md-card *ngFor="let event of events | async"> 
    <a [routerLink]="['event', event?.slug]"><img class="event-img" src="http://lorempixel.com/30/30" />{{ event?.name }}</a> 
</md-card>