Snippets from the Firestore Data Modeling Course

config.js

import * as firebase from 'firebase/app';
import 'firebase/firestore';

var firebaseConfig = {
  // your firebase credentials
};


  // Initialize Firebase
firebase.initializeApp(firebaseConfig);

export const db = firebase.firestore();

many-to-many.js

import { db } from './config';

const authorId = 'dr-seuss';
const bookId   = 'lorax';

// 7. Middle Man Collection
const userReviews = db.collection('reviews').where('author', '==', authorId);
const bookReviews = db.collection('reviews').where('book', '==', bookId);

// Single read with composite key
const specificReview = db.collection('reviews').doc(`${bookId}_${authorId}`);


// 8. Map
// Reviews embadded on books
const bookWithReviews = db.collection('books').doc(bookId);
const userReviews = db.collection('books').orderBy('reviews.jeff-delaney');


// 9. Array
const books = db.collection('books').where('categories', 'array-contains', 'fiction');



// 10. Bucket
// Get a collection of documents with an array of IDs

const getLikedBooks = async() => {

    // Get users through book likes
    const bookLikes = await db.collection('likes').doc(bookId).get();
    const userIds = Object.keys( bookLikes.data() );
    const userReads = userIds.map(id => db.collection('authors').doc(id).get() );
    const users = await Promise.all(userReads).then(console.log);

    // Get books through user likes
    const userLikes = await db.collection('likes').orderBy('jeff-delaney').get();
    const bookIds = userLikes.docs.map(snap => snap.id);

    const bookReads = bookIds.map(id => db.collection('books').doc(id).get() );
    const books = Promise.all(bookReads).then(console.log);
}


getLikedBooks()

one-to-many.js

import { db } from './config';

const authorId = 'dr-seuss';


// 4. Embedded One-to-Many
const authorWithBooks = db.collection('authors').doc(authorId)


// 5. Subcollection
const books = db.collection('authors').doc(authorId).collection('books');



// 6. Root Collection, requires index
const booksFrom1971 = db.collection('books')
    .where('author', '==', authorId)
    .where('published', '>', 1971);

one-to-one.js

import { db } from './config';

const userId = 'ayn-rand';

// 1. Embedded, all data contained on single document, One-to-few

const authorWithAccount = db.collection('authors').doc(userId)

// 2. Shared Document ID
const author = db.collection('authors').doc(userId)
const account = db.collection('account').doc(userId);


// 3. Join related documents with different IDs, 
const getAccount = async (userId) => {
    const snapshot = await db.collection('authors').doc(userId).get();
    const user = snapshot.data();

    return db.collection('accounts').doc(user.accountId)
}

query.js

import { db } from './config';

// Single Doc Read
const ref = db.collection('posts').doc('postId')

// Subcollection Read
const ref = db.collection('posts').doc('postId').collection('tags');


// Bucket Read

const post = db.collection('posts').doc('postId')
const tags = db.collection('tags').doc('postId')


// Multi-document read

const post = await db.collection('posts').doc('postId').get();

const tagIds = post.data().tags;

const tagReads = tagIds.map(tag => db.collection('tags').get(tag));

const tags = await Promise.all(tagReads);


// Helper: Reads an array of IDs from a collection concurrently
const readIds = async (collection, ids) => {
    const reads = ids.map(id => collection.doc(id).get() );
    const result = await Promise.all(reads);
    return result.map(v => v.data());
}

social-feed.js

    
import { db } from './config';
import * as firebase from 'firebase/app';
const remove = firebase.firestore.FieldValue.arrayRemove;
const union = firebase.firestore.FieldValue.arrayUnion;

export const follow  = (followed, follower) => {
    const followersRef = db.collection('followers').doc(followed);

   followersRef.update({ users: union(follower) });
}

// 2. Unfollow User

export const unfollow  = (followed, follower) => {
    const followersRef = db.collection('followers').doc(followed);

    followersRef.update({ users: remove(follower) });
}



// 3. Get posts of followers

export const getFeed = async() => {

    const followedUsers = await db.collection('followers')
        .where('users', 'array-contains', 'jeffd23')
        .orderBy('lastPost', 'desc')
        .limit(10)
        .get();


    const data = followedUsers.docs.map(doc => doc.data());

    const posts = data.reduce((acc, cur) => acc.concat(cur.recentPosts), []);
 

    const sortedPosts = posts.sort((a, b) => b.published - a.published)


    // render sortedPosts in DOM

}

I think to use it for my web app https://truckercheckin.com

Are you going to update to v9 syntax?