Using Firestore with Typescript

firestore.ts

/**
 * This Gist is part of a medium article - read here:
 * https://jamiecurnow.medium.com/using-firestore-with-typescript-65bd2a602945
 */

// import firstore (obviously)
import { firestore } from "firebase-admin"

// Import or define your types
// import { YourType } from '~/@types'
interface YourType {
  firstName: string
  lastName: string
  isGreat: boolean
  blackLivesMatter: true
}

interface YourOtherType {
  something: boolean
  somethingElse: boolean
}

// This helper function pipes your types through a firestore converter
const converter = <T>() => ({
  toFirestore: (data: Partial<T>) => data,
  fromFirestore: (snap: FirebaseFirestore.QueryDocumentSnapshot) => snap.data() as T
})

// This helper function exposes a 'typed' version of firestore().collection(collectionPath)
// Pass it a collectionPath string as the path to the collection in firestore
// Pass it a type argument representing the 'type' (schema) of the docs in the collection
const dataPoint = <T>(collectionPath: string) => firestore().collection(collectionPath).withConverter(converter<T>())

// Construct a database helper object
const db = {
  // list your collections here
  users: dataPoint<YourType>('users'),
  userPosts: (userId: string) => dataPoint<YourOtherType>(`users/${userId}/posts`)
}

// export your helper
export { db }
export default db

/**
 * Some examples of how to use:
 */

const example = async (id: string) => {
  // firestore just as you know it, but with types
  const userDoc = await db.users.doc(id).get()
  const { blackLivesMatter } = userDoc.data()
  return blackLivesMatter === true // obviously
}

const createExample = async (userId: string) => {
  await db.userPosts(userId).doc().create({
    something: false,
    somethingElse: true
  })
}

// Always use set for updates as firestore doesn't type update function correctly yet!
const updateExample = async (id: string) => {
  await db.users.doc(id).set({
    firstName: 'Jamie',
    blackLivesMatter: true
  }, { merge: true })
}

I can't destruct the typed object returning from doc.data().

export interface User {
  id: number;
  name: string;
  email: string;
}

// omitting converter & dataPoint functions

const db = {
  users: dataPoint<User>("users"),
};

Then in a Cloud Function I have:

const userDoc = await db.users.doc("12345").get();
const { email } = userDoc.data(); // error message: "Property 'email' does not exist on type 'Partial<User> | undefined'"

This should pretty much do the trick of having typed results from Firestore, however, the error message above keeps preventing typescript from compiling the code.

Any thoughts on this?

Thanks!