Clean up Firestore and Storage when deleting a document

When you delete a document in Firestore, its subcollections and their documents are not automatically recursively deleted. Here is a simple Cloud Function that takes care of it. As a bonus, it also deletes all stored files in Firebase Storage in a folder with the same name as the document id.

const functions = require("firebase-functions");
const admin = require("firebase-admin");
admin.initializeApp();
const client = require("firebase-tools");
const bucket = admin.storage().bucket("gs://your-bucket.appspot.com");

exports.onDeleteCampaign = functions.firestore
  .document("campaigns/{campaignId}")
  .onDelete((snap, context) => {
    const campaignId = context.params.campaignId;

    // Delete all nested sub collections
    const prom1 = client.firestore.delete(`campaigns/${campaignId}`, {
      project: process.env.GCLOUD_PROJECT,
      recursive: true,
      yes: true,
    });

    // And delete any uploaded images
    const prom2 = deleteFiles(campaignId);

    return Promise.all([prom1, prom2]);
  });

async function deleteFiles(campaignId) {
  const options = {
    prefix: `campaign/${campaignId}`,
  };

  const [files] = await bucket.getFiles(options);
  const deletePromises = files.map(file => file.delete());
  return Promise.all(deletePromises);
}

For example in my case all images for a campaign are stored as campaign/{campaignId}/subfolder/filename, and that makes it easy to delete all images using the Cloud Function above.