Using Firestore with Typescript - including update helper

firestore.ts

/**
 * This Gist is part of a medium article - read here:
 * https://jamiecurnow.medium.com/using-firestore-with-more-typescript-8058b6a88674
 */

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

// Here's the helper type for paths:
type PathImpl<T, K extends keyof T> =
  K extends string
  ? T[K] extends Record<string, any>
  ? T[K] extends ArrayLike<any>
  ? K | `${K}.${PathImpl<T[K], Exclude<keyof T[K], keyof any[]>>}`
  : K | `${K}.${PathImpl<T[K], keyof T[K]>}`
  : K
  : never

type Path<T> = PathImpl<T, keyof T> | keyof T

type PathValue<T, P extends Path<T>> =
  P extends `${infer K}.${infer Rest}`
  ? K extends keyof T
  ? Rest extends Path<T[K]>
  ? PathValue<T[K], Rest>
  : never
  : never
  : P extends keyof T
  ? T[P]
  : never

type UpdateData<T extends object> = Partial<{
  [TKey in Path<T>]: PathValue<T, TKey>
}>

// Import or define your types
// import { User } from '~/@types'
interface User {
  name: string
  email: string
  address: {
    line1: string
    line2: string
    postcode: string
    verified: false
    timeAtAddress: {
      days: string
      months: string
      hours: string
    }
  }
}

interface Post {
  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<User>('users'),
  userPosts: (userId: string) => dataPoint<Post>(`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 { address } = userDoc.data()
  return address.line1
}

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

const updateExample = async (id: string) => {
  const updates: UpdateData<User> = {
    "address.line1": '',
    name: ''
  }
  await db.users.doc(id).update(updates)
}