使用AngularFire2获取Firebase节点的孩子数量？ [英] Get number of children for a Firebase node using AngularFire2?

问题描述

我需要统计Firebase中多个子树的子节点数，以便在视图中显示。对于上下文，我的应用程序正在统计用户在一个进程的不同阶段。

我的根节点（stage）有两个子树（stageOne，stageTwo）。每个子树都包含一个可变数量的子节点，我需要在视图中进行计数和显示。

数据库：

 阶段
 | __stageOne 
 | | __user1 
 | | __user2 
 | 
 | __stageTwo 
 | __user3 
  

组件：

  stageObject：FirebaseObjectObservable< any>; 
 
构造函数（public af：AngularFire）{
 this.stageObject = af.database.object（'/ stages'）; 
 
 
 
 $ b $ p $查看（不显示）
 
 
 < h3>第1阶段计数= {{（stageObject | async）?. stages.stageOne.length}}< / h3> 
< h3>第2阶段计数= {{（stageObject | async）?. stages.stageTwo.length}}< / h3> 
  
查看（应该是这样）：
 
 
 第1阶段计数= 2 
第2阶段计数= 1 
  
 
 
 class =lang-ts prettyprint-override>  this.http.get（'https://your-app-name.firebaseio.com/stages/stageOne.json?shallow=true'）
 .map（response => response.json（））
 .subscribe（items => Object.keys（items）.length）
  

使用 shallow = true 节点。

$ hr



如果要加载所有这些元素，可以使用 list / code>：

$ b

  this.stageOneObject = af.database.list（'/阶段/ stageOne'）; 
  

或将对象转换为数组：

  this.stageOneObject = Object.keys（this.stageObject.stageOne）
 .map（key => this.stageObject.stageOne [key]） ; 
  

I need to count the number of children nodes for multiple subtrees in Firebase to display in the view. For context, my app is counting users at different stages in a process.

My root node (stages) has two subtrees (stageOne, stageTwo). Each subtree contains a variable number of child nodes which I need to count and display in the view.

Database:

stages
|__stageOne
|  |__user1
|  |__user2
|
|__stageTwo
   |__user3

Component:

stageObject: FirebaseObjectObservable<any>;

constructor(public af: AngularFire){
    this.stageObject = af.database.object('/stages');
}

View (doesn't display)

<h3>Stage 1 Count = {{ (stageObject | async)?.stages.stageOne.length }}</h3>
<h3>Stage 2 Count = {{ (stageObject | async)?.stages.stageTwo.length }}</h3>

View (how it should look):

Stage 1 Count = 2
Stage 2 Count = 1

解决方案

You can't get count with AngularFire2 (without loading all items), but you can use REST API:

this.http.get('https://your-app-name.firebaseio.com/stages/stageOne.json?shallow=true')
  .map(response => response.json())
  .subscribe(items => Object.keys(items).length)

Using shallow=true will return just keys for all children for 'selected' node.

---

If you want to load all of them, you can use list():

this.stageOneObject = af.database.list('/stages/stageOne');

or transform object to array:

this.stageOneObject = Object.keys(this.stageObject.stageOne)
                            .map(key => this.stageObject.stageOne[key]);

这篇关于使用AngularFire2获取Firebase节点的孩子数量？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！