AngularFire2在数组中嵌套了* ngFor数组...但是Firebase没有数组...? [英] AngularFire2 nested *ngFor Array within Array... but Firebase doesn't have arrays...?

问题描述

我正在使用AngularFire2，试图将列表从列表中取出. * ngFor中的嵌套* ngFor不会显示在视图中...

I'm using AngularFire2, trying to get lists out of lists. A nested *ngFor within an *ngFor doesn't show on the view...

app.componnent

app.componnent

...
constructor(private _af: AngularFire) {
    this.lists = this._af.database.list(this._API_URL);
}
...

app.component.html

app.component.html

<div *ngFor="let list of lists | async">
    {{sublist.name}}<br/> <!-- I can see you -->

    <!--******* I can't see you **********-->
    <div *ngFor="let rootword of list.rootwords">
        {{rootword.word}} {{rootword.total}}
    </div> 
</div>

Firebase示例

Example of Firebase

maindb
  |_list1
  |  |_name: 'List 1"
  |  |_rootwords
  |     |_apple
  |     |   |_word: 'apple'
  |     |   |_total: 4
  |     |
  |     |_banana
  |     |   |_word: 'banana'
  |     |   |_total: 2
  |     |_carpet 
  |     |   |_word: 'carpet'
  |     |   |_total: 21
  |
  |_list2
     |_name: "List 2"
     |_rootwords
        |_elephant
        |    |_word: 'elephant'
        |    |_total: 4
        |_sloth
             |_word: 'sloth
             |_total: 5

如何使用firebase.list将ngFor嵌套在ngFor中? 我需要地图或过滤器吗? AngularFire2是否可以将内部对象转换为数组?

How do you nest an ngFor in an ngFor with firebase.list ?? Do I need to map or filter? Does AngularFire2 have a way to convert the inner object to an array?

感谢所有建议！

推荐答案

您可以使用rootwords对象="nofollow noreferrer"> map运算符和 Array.prototype.reduce ，如下所示:

You can replace the rootwords object with an array using the map opererator and Array.prototype.reduce, like this:

import 'rxjs/add/operator/map';

constructor(private _af: AngularFire) {

  this.lists = this._af.database
    .list(this._API_URL)

    // Use map the map operator to replace each item in the list:

    .map(list => list.map(item => ({

      // Map to a new item with all of the item's properties:
      ...item,

      // And replace the rootwords with an array:
      rootwords: Object.keys(item.rootwords)

        // Use reduce to build an array of values:
        .reduce((acc, key) => [...acc, item.rootwords[key]], [])
      })
    ));
}

或者，不使用传播语法:

Or, without the spread syntax:

import 'rxjs/add/operator/map';

constructor(private _af: AngularFire) {

  this.lists = this._af.database
    .list(this._API_URL)
    .map(list => list.map(item => {
        var copy = Object.assign({}, item);
        copy.rootwords = Object.keys(item.rootwords).reduce((acc, key) => {
            acc.push(item.rootwords[key]);
            return acc;
        }, []);
        return copy;
    }));
}

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