firebase-function-example.ts

authorUpdate.ts

import * as functions from 'firebase-functions'
import * as admin from 'firebase-admin'

interface AuthorData {
  role: string;
  name: string;
}

const onAuthorNameUpdated = functions.firestore.document('users/{userId}').onWrite(async (change, context) => {
  if (!change.after.exists) {
    // skip
    return
  }

  const data = change.after.data() as AuthorData;
  const previous = change.before.data() as AuthorData;

  // skip non-authors
  if (data.role !== 'author' && data.role !== 'admin') {
    return;
  }

  // skip if no name update
  if (previous.name === data.name) {
    return;
  }

  console.log(`Author '${previous.name}' changed name to '${data.name}', updating all articles`);
  
  const snapshot = await admin.firestore().collection('articles')
    .where('authorId', '==', change.after.id)
    .get();

  const updates = snapshot.docs.map((doc) => admin.firestore().doc(`articles/${doc.id}`).update({'author': data.name }))
  await Promise.all(updates)

  console.log(`Updated ${updates.length} articles!`)
})

export = onAuthorNameUpdated;