迭代Firebase值

Question

我想访问comments数组并进行一些计算以得出评分（avgstars）的平均值，并显示我的Firebase数组中特定项目的评论数。

任何想法？

ngOnInit() {
  this.route.params
    .pipe(switchMap((params: Params) => this.dishservice.getDish(params['id'])))
    .subscribe(dish => {
      this.dish = dish
      this.favorite = this.favoriteService.isFavorite(this.dish.id); 

      //compute the average of the comments and the render the length of the array
      this.numcomments = /* This is the locus --->*/ this.dish.comments.length;           
      let total =0; 
      this.dish.comments.forEach(comment =>total += comment.rating); 
      this.avgstars = (total/this.numcomments).toFixed(2); 
         },
        errmess => this.errMess = <any>errmess); 
      }

这里是数据样本

Answer 1

看起来“ comments”是一个对象，not是一个数组。因此，您将无法通过“长度”获得数字。

您可以尝试通过对象键进行迭代。

参见此处：How do I loop through or enumerate a JavaScript object?

Answer 2

You don't have change your firebase data model as long as you create a new Array by iterating your "key" (-M8V...) values from the "comments" object.

I would do something like this:

let p = this.dish[0].comments;
for (let [key, value] of Object.entries(p)) {
  console.log(key, value);
}