Firebase: joining tables

Question

Assume that the data look like this

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

author: {
  uid: '123AA',
  displayName: 'Richard'
  email: '[email protected]'
}

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()})
})

Answer 1

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