Angular2中的嵌套Observable使用AngularFire2不在视图中渲染 [英] Nested Observables in Angular2 using AngularFire2 not rendering in view

问题描述

我正在构建一个使用Firebase和AngularFire2（目前处于alpha版）的实验性（Ionic 2）应用。为此，我将以Aaron Saunders的教程为基础：

I'm building an experimental (Ionic 2) app that uses Firebase and AngularFire2 (currently in alpha). For this I'm following this tutorial from Aaron Saunders as a basis:

http://www.clearlyinnovative.com/integrating-firebase-with-angularfire2-into-angular2-ionic2-part-2
https://github.com/aaronksaunders/ionic2-angularfire-sample

以下是我的home.ts和我的home.html。

Below are my home.ts and my home.html.

this.projects = af.list('/items').map( (items) => {
    return items.map( item => {
        item.meta = af.object(`/item_meta/${item.$key}`)
        return item
    })
})

以下演示文稿演示了AngularFire2嵌套Observables返回的方法：< a href =https://youtu.be/ngnSOTSS8Q8?t=1h6m37s\"rel =noreferrer> https://youtu.be/ngnSOTSS8Q8?t=1h6m37s

This way of nesting the Observables returns by AngularFire2 was demonstrated in the following presentation: https://youtu.be/ngnSOTSS8Q8?t=1h6m37s

以下是我的观点：

<ion-card *ngFor="#item of items | async">
    <ion-card-header>
        {{item.name}}
    </ion-card-header>
    <ion-card-content>
        {{item.description}}
        <br>

        {{item.meta.stockPrice | async}}

    </ion-card-content>
</ion-card>

我所遵循的演示中的示例的主要区别在于我正在筑巢'对象'可观察的'列表/数组'可观察。相反，他们在列表中添加一个列表。这样做的结果是我试图直接在我的视图中渲染{{item.meta.stockPrice}}而不是嵌套一个ngFor。

The main difference with the example in the presentation I followed is the fact that I'm nesting an 'object' Observable inside an 'list/array' Observable. Instead they add a list within a list. The consequence of this is that I'm trying to render {{ item.meta.stockPrice }} in my view directly instead of nesting an ngFor.

这就是我的意思数据如下：

This is what my data looks like:

{
    "items":
        {
            "item1":{
                "name": "Item 1",
                "description": "1234"
            },
            "item2":{
                "name": "Item 2",
                "description": "abcd"
            }
        }
    "items_meta"{
        "item1":{
            "stockPrice": 1234,
            "moarData": "derp"
        },
        "item2":{
            "stockPrice": 386,
            "moarData": "lolz"
        }
    }
}

我似乎无法弄清楚为什么对象不想渲染。如果我将其输出到JSON，它会显示数据存在。请注意，我是Angular2的新手，仍然围绕着Angular1的变化。我做错了什么？

I can't seem to figure out why object doesn't want to render. If I output it to JSON it shows that the data is there. Please note that I am new to Angular2 and still wrapping my head around the changes from Angular1. What am I doing wrong?

编辑：我更新了上面的信息并添加了我的数据结构以使其更清晰

I've update the info above and added my data structure to make it more clear

推荐答案

针对您的具体问题......

For your specific issue...

{{(item.meta | async)?.stockPrice}}

使用elvis运算符（ ？）确保 async 操作完成，然后访问所需的值

use the elvis operator (?) to make sure the async operation is complete and then access the desired value

github中的源代码： https://github.com/aaronksaunders/afwithngcli

source code here in github: https://github.com/aaronksaunders/afwithngcli

-

你领先我......在新博客上发帖，但这里是代码

you got ahead of me... working on the new blog post, but here is the code

script.html

</ion-card>
    <ion-card *ngFor="#user of usersWithMessages | async">
    <ion-card-header>
        {{user.displayName}}
    </ion-card-header>
    <ion-card-content>
       {{ (user.messages | async) | json}}
    </ion-card-content>
</ion-card>

script.ts

this.usersWithMessages = this.af.list('/users').map((_users) => {
    return _users.map((_user) => {
        _user.messages = this.af.object("/userObjects/public-messages/" +_user.$key)
        return _user
    })
})

数据

   "userObjects" : {
    "public-messages" : {
      "8d75a63e-80cd-40cc-8f8b-87d3d33b0cd0" : {
        "message-id-0" : {
          "text" : "a public message"
        }
      },
      "9c6ea912-ec24-4127-b123-6512ed135f06" : {
        "-KFCGp5ojo7JSX2myOPE" : {
          "date" : "1460511658442.75",
          "text" : "this should be a. public message"
        },
        "-KFCJc4GtEo_PDWi7hru" : {
          "date" : "1460512391529.69",
          "text" : "this is a message that should be public"
        },
        "message-id-100" : {
          "date" : "3243245411111",
          "text" : "public for the other user"
        }
      }
    }
  },
 "users" : {
    "8d75a63e-80cd-40cc-8f8b-87d3d33b0cd0" : {
      "displayName" : "[e-mail]",
      "provider" : "password"
    },
    "9c6ea912-ec24-4127-b123-6512ed135f06" : {
      "displayName" : "[e-mail]",
      "provider" : "password"
    },
    "cdcf32af-a8cd-467d-a04f-dfc223e890d2" : {
      "avatar" : "https://secure.gravatar.com/avatar/d23563ab3014ce965a90c37b22a34da8?d=retro",
      "displayName" : "[e-mail]",
      "provider" : 4
    }
  }

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