Version: 2020fa

Lecture 3

Lecture Video

Lecture Slides

Assignment 2 due 10/13 03:59pm

Before the lecture#

Install Postman#

Install Postman from https://www.postman.com/downloads/ If necessary, set up a Postman account using your Cornell email address.

Firebase Setup#

  1. Create an account on Firebase. You only need the free version.
  2. Go to Firebase console and click Add project. Choose any random name for the project name. You won't need Google Analytics in this class but it is fine to enable it. Analytics location doesn't matter, leave it at default United States and check the remaining boxes agreeing to terms and click Create project.
  3. Once your project is created, go into it and go to the Database tab under Develop. Choose to create database starting in production mode. Keep the Firestore location as default.
  4. Download the service account in Project Settings > Service accounts as service-account.json. Project Settings can be found by clicking the gear button on the left panel next to Project Overview. Go to Service accounts tab and click the Generate new private key button. Save the downloaded file as service-account.json This json should be kept secret.

Check your setup#

Code#

Create a folder with the following package.json and index.ts. Put the downloaded service-account.json in this folder.

Also add tsconfig.json, which you can find in Lecture 2 notes.

Copy the following code into package.json.

package.json
{
"name": "self-check",
"version": "0.1.0",
"main": "index.ts",
"license": "MIT",
"scripts": {
"tsc": "tsc -p tsconfig.json",
"start": "yarn tsc && node output/index"
},
"dependencies": {
"body-parser": "^1.18.3",
"express": "^4.17.1",
"firebase-admin": "^9.2.0"
},
"devDependencies": {
"@types/express": "^4.17.8",
"@types/node": "^14.11.5",
"typescript": "^4.0.3"
}
}

Copy the following code into index.ts. Remember to replace databaseURL with the url of your own. You can find this databaseURL in the code snippet in the service accounts tab of Firebase.

Don't worry if you don't understand this code! You'll know what it does and how to write similar code by the end of this course!

index.ts
import admin from 'firebase-admin';
import express from 'express';
import bodyParser from 'body-parser';
// Path to wherever you put your service-account.json
const serviceAccount = require('../service-account.json');
admin.initializeApp({
credential: admin.credential.cert(serviceAccount),
databaseURL: '[YOUR_OWN_DATABASE_URL]',
});
const db = admin.firestore();
const app = express();
const port = 8080;
app.use(bodyParser.json());
app.get('/', (_, res) => res.send('Hello World!'));
app.get('/self-check', async (_, resp) => {
const data = {
name: 'Hello World',
time: admin.firestore.FieldValue.serverTimestamp(),
};
console.log('Sending doc to DB.');
await db.collection('test').doc('random-id').set(data);
console.log('Doc recorded in DB');
const docRef = db.collection('test').doc('random-id');
console.log('Trying to obtain doc in DB.');
const docSnapshot = await docRef.get();
console.log(
`We obtained a doc with id ${docSnapshot.id}. It's content is logged below:`
);
console.log(docSnapshot.data());
console.log('Now we will try to remove it.');
await docRef.delete();
console.log('The document is deleted.');
console.log(
'After all these operations, the db should be empty. We check that.'
);
db.collection('test')
.get()
.then((querySnapshot) => {
if (querySnapshot.docs.length === 0) {
console.log('We passed the check. The page in browser should say OK.');
resp.status(200).send('OK.');
} else {
console.log('We failed the check. Please check your setup.');
resp.status(500).send('Something is messed up!');
}
});
});
app.listen(port, () => console.log(`Example app listening on port ${port}!`));

Verify that it works#

  1. Run yarn install;
  2. Run yarn start;
  3. Open http://localhost:8080. You will see Hello World!;
  4. Open http://localhost:8080/self-check. You will see OK! in the browser. In the terminal, you will see something like this:
Example app listening on port 8080!
Sending doc to DB.
Doc recorded in DB
Trying to obtain doc in DB.
We obtained a doc with id random-id. It's content is logged below:
{
name: 'Hello World',
time: Timestamp { _seconds: 1602132872, _nanoseconds: 588000000 }
}
Now we will try to remove it.
The document is deleted.
After all these operations, the db should be empty. We check that.
We passed the check. The page in browser should say OK.

Basic Database Manipulations#

People usually call that CRUD, which stands for:

  • Create/Insert - Create a document (will fail if the document exists)
  • Read/Find/Query - To search for documents based on their properties
  • Update - Update an existing document (will fail otherwise)
  • Delete - Delete an existing document

For convenience, most NoSQL database also provides an upsert operation. It will create the document or update an existing document. You can think of that as an atomic operation that does:

if (document.exists()) {
database.update(document);
} else {
database.insert(document);
}

In Firestore, you can either insert a new document with a specified ID, or allow Firestore to generate its own ID for you.

The update method in Firestore allows you to update certain fields of the document without overwriting the entire thing.

Sample code#

The following code demonstrate how we can do basic CRUD with Firestore. Note that the code below does not care about what are the fields of a post, because Firestore doesn't require you to have a predefined set of fields. This gives you flexibility when writing your backend code.

index.ts
// in typescript import packages as modules
import admin from 'firebase-admin';
import express from 'express'; // also install type aliases for Request, Response
import bodyParser from 'body-parser';
const serviceAccount = require('./service-account.json');
admin.initializeApp({
credential: admin.credential.cert(serviceAccount),
databaseURL: '[DATABASE_URL]',
});
const db = admin.firestore();
const app = express();
const port = 8080;
app.use(bodyParser.json());
// Define a type for our Post document stored in Firebase
type Post = {
content: string;
name: string;
};
// Add id field to our Post type
type PostWithID = Post & {
id: string;
};
app.get('/', (_, res) => res.send('Hello World!'));
const postsCollection = db.collection('posts');
// create a post
app.post('/post', async function (req, res) {
const post: Post = req.body;
const myDoc = postsCollection.doc();
await myDoc.set(post);
res.send(myDoc.id);
});
// read all posts
app.get('/post', async function (_, res) {
// we don't use the first request parameter
const allPostsDoc = await postsCollection.get();
const posts: PostWithID[] = [];
for (let doc of allPostsDoc.docs) {
let post: PostWithID = doc.data() as PostWithID;
post.id = doc.id;
posts.push(post);
}
res.send(posts);
});
// read posts by name
app.get('/post/:name', async function (req, res) {
const namePostsDoc = await postsCollection
.where('name', '==', req.params.name)
.get();
const posts: PostWithID[] = [];
for (let doc of namePostsDoc.docs) {
let post: PostWithID = doc.data() as PostWithID;
post.id = doc.id;
posts.push(post);
}
res.send(posts);
});
// sorted posts by name
app.get('/postsorted', async function (_, res) {
// we don't use the first request parameter
const sortedPosts = await postsCollection.orderBy('name', 'desc').get();
const posts: PostWithID[] = [];
for (let doc of sortedPosts.docs) {
let post: PostWithID = doc.data() as PostWithID;
post.id = doc.id;
posts.push(post);
}
res.send(posts);
});
// update a post
app.post('/post/:id', async function (req, res) {
const id: string = req.params.id;
const newPost = req.body;
await postsCollection.doc(id).update(newPost);
res.send('UPDATED');
});
// delete a post
app.delete('/post/:id', async function (req, res) {
const id: string = req.params.id;
await postsCollection.doc(id).delete();
res.send('DELETED');
});
app.listen(port, () => console.log(`Example app listening on port ${port}!`));