Firebase：连接表格 [英] Firebase: joining tables

问题描述

假设数据看起来像这样

  post：{
 authorId：'123AA'，
 title：'first post'，
 body：'yay'
} 
 
作者：{
 uid：'123AA'，
 displayName：' Richard'
 email：'[e-mail]'
} 
  

I

 < div className =post>想要使用作者的名字来显示帖子：
 
< div className =title> {post.title}< / div> 
< div className =body> {post.body}< / div> 
< div className =author-name> {post.author.displayName}< / div> //问题
< / div> 
  

取得的项目只包含作者的 uid ，但是我需要作者的 displayName 。检索帖子时如何填充作者字段？这是我现在要做的职位：

$ p $ const postsRef = firebase.database（）。ref（'posts / '）
postsRef.on（'value'，（snapshot）=> {
this.setState（{posts：snapshot.val（）}）
}）


解决方案

在真实的firebase中不确定，但我经常在angular2中使用join。这里我的示例代码。
$ b

 从'@ angular / core'导入{Component，OnInit}; 
从'angularfire2'导入{AngularFire}; 
从'rxjs / Observable'导入{Observable}; 
导入'rxjs / add / operator / map'; 
 
 @Component（{
 selector：'app'，
 templateUrl：`
< ul> 
< li * ngFor =let p | async> 
 {{p.title}}  -  {{p.authorName | async）？displayName}} 
< / li> 
< / ul> ; 
`
}）
 export class InitComponent implements OnInit {
 posts：Observable< any []>; 
 
构造函数（private af：AngularFire）{} 
 
 ngOnInit（）{
 this.posts = this.af.database.list（'/ posts'） 
 .map（posts => {
 posts.map（p => {
 p.authorName = this.af.database.object（'/ authors /'+ p.authorId ）; 
}）; 
返回信息; 
}）; 
 
 
 
 
 
 
数据库结构如下：
 
 pre $  / posts / postId / {authorId，title，body} 
 / authors / authorId / {displayName，email} 
  

希望这有助于

Assume that the data look like this

post: {
  authorId: '123AA',
  title: 'first Post',
  body: 'yay'
}

author: {
  uid: '123AA',
  displayName: 'Richard'
  email: '[e-mail]'
}

I want to render a post with the author's name:

<div className="post">
  <div className="title">{post.title}</div>
  <div className="body">{post.body}</div>
  <div className="author-name">{post.author.displayName}</div> //problem
</div>

A fetched post item only contains an author's uid, but I need the author's displayName. How do I populate the author field when retrieving the posts? This is what I do to fetch the posts right now:

const postsRef = firebase.database().ref('posts/')
postsRef.on('value', (snapshot) => {
  this.setState({posts: snapshot.val()})
})

解决方案

Not sure in real firebase, but I use join quite often in angular2. Here my sample code.

import { Component, OnInit } from '@angular/core';
import { AngularFire } from 'angularfire2';
import { Observable } from 'rxjs/Observable'; 
import 'rxjs/add/operator/map';

@Component({
  selector: 'app',
  templateUrl: `
    <ul>
        <li *ngFor="let p of posts | async">
            {{ p.title }} - {{ (p.authorName | async)?.displayName }}
        </li>        
    </ul>
`
})
export class InitComponent implements OnInit {
    posts: Observable<any[]>;

  constructor(private af: AngularFire) {}

  ngOnInit() {
      this.posts = this.af.database.list('/posts')
      .map(posts => {
          posts.map(p => {
              p.authorName = this.af.database.object('/authors/'+p.authorId);
          });
          return posts;
      });
  }

The database structure as follows:

/posts/postId/{authorId, title, body}
/authors/authorId/{displayName, email}

Hope this helps

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