Firebase 列表的嵌套 Angular2 ngFor 指令 [英] Nested Angular2 ngFor Directives for Firebase Lists

问题描述

我想在 Angular 2 中使用 ngFor 将 Firebase 查询的结果绑定到我的模板.这很容易在下面实现.

组件:

导出类FeaturedThreadsComponent {线程:FirebaseListObservable;质量主题:主题<任何>；构造函数(AF:AngularFire){this.qualitySubject = new Subject();this.threads = af.database.list('/threads', {询问: {orderByChild: '质量',结束时间:5}});}}

模板:

{{thread.title}}

但是如果我想使用另一个嵌套在模板中的 ngFor 指令来列出子对象的键...

{{thread.title}}<div *ngFor="让 thread.participants 的参与者">{{参与者.$key}}}

我收到控制台错误，找不到类型为object"的不同支持对象[object Object]".NgFor 只支持绑定到 Iterables，比如 Arrays.

在我的数据库结构中，participants 是thread 的一个孩子，它是threads 的一个孩子，其中thread 是一个动态键.所以我不能使用 participants 的直接路径.

这种嵌套 ngFor 指令的模式在一个简单地迭代本地文件的服务中工作得很好.为什么它在这里不起作用对我来说似乎有点模糊.

解决方案

对于那些关注此线程到它被标记为重复的线程的人，请不要像接受的答案所建议的那样创建管道.最佳答案避免了已接受答案的性能问题，而且要简单得多.

I want to bind the results of a Firebase query to my template using ngFor in Angular 2. This is easily achieved below.

component:

export class FeaturedThreadsComponent { 
    threads: FirebaseListObservable<any[]>;
    qualitySubject: Subject<any>;

    constructor(af: AngularFire) {
        this.qualitySubject = new Subject();
        this.threads = af.database.list('/threads', {
            query: {
                orderByChild: 'quality',
                endAt: 5
            }
        });
    }
}

template:

<div *ngFor="let thread of threads | async">
    {{thread.title}}
</div>

But if I want to use another ngFor directive nested within the template to list a child object's keys...

<div *ngFor="let thread of threads | async">
    {{thread.title}}
    <div *ngFor="let participant of thread.participants">
        {{participant.$key}}}
    </div>
</div>

I get the console error, Cannot find a differ supporting object '[object Object]' of type 'object'. NgFor only supports binding to Iterables such as Arrays.

In my database structure, participants is a child of thread, which is a child of threads where thread is a dynamic key. So I can't use a direct path to participants.

This pattern of nesting ngFor directives worked fine in a service that simply iterated over a local file. Why it isn't working here seems a bit fuzzy to me.

解决方案

For those of you who follow this thread to the one it is flagged as a duplicate of, resist creating a pipe like the accepted answer suggests. The best answer avoids the performance issues of the accepted answer and is much simpler.

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