Copy object from one node to another in Cloud Functions for Firebase

Question

I'm using Cloud Functions for Firebase, and I'm stuck with what seems to be a very basic operation.

If someone adds a post, he writes to /posts/. I want a portion of that post to be saved under a different node, called public-posts or private-posts, using the same key as was used in the initial post.

My code looks like this

const functions = require('firebase-functions');

exports.copyPost = functions.database
  .ref('/posts/{pushId}')
  .onWrite(event => {
    const post = event.data.val();
    const smallPost = (({ name, descr }) => ({ name, descr }))(post);
    if (post.isPublic) {
      return functions.database.ref('/public-posts/' + event.params.pushId)
        .set(smallPost);
    } else {
      return functions.database.ref('/private-posts/' + event.params.pushId)
        .set(smallPost);
    }
  })

The error message I get is: functions.database.ref(...).set is not a function.

What am I doing wrong?

Answer 1

If you want to make changes to the database in a database trigger, you either have to use the Admin SDK, or find a reference to the relevant node using the reference you've been given in the event. (You can't use functions.database to find a reference - that's used for registering triggers).

The easiest thing is probably to use event.data.ref (doc) to find a reference to the location you want to write:

const root = event.data.ref.root
const pubPost = root.child('public-posts')