How to clone a node to another path based on a reference value from the initial path on Google Cloud Functions?

Question

I am trying clone an "original" node's data (as soon as I create the data) to a path that is based on the original node's path.

This is my data structure:

root: { 
  doors: {
    111111111111: {
       MACaddress: "111111111111",
       inRoom: "-LBMH_8KHf_N9CvLqhzU", // I will need this value for the clone's path
       ins: {
          // I am creating several "key: pair"s here, something like:
          1525104151100: true,
          1525104151183: true,
       }
    }
  },
  rooms: {
    -LBMH_8KHf_N9CvLqhzU: {
      ins: {
        // I want the function to clone the same data here:
        1525104151100: true,
        1525104151183: true,
      }
    }
  }

My cloud function is now like this:

exports.updateRoom = functions.database.ref('/doors/{MACaddress}/ins').onWrite((change, context) => {
    const beforeData = change.before.val(); // data before the write
    const afterData = change.after.val(); // data after the write
    const roomPushKey = change.before.ref.parent.child('/inRoom');
    console.log(roomPushKey); // this is retrieving all the info about the ref "inRoom" but not its value... 

Question 1) How can I get to this ref/node's value?

My code goes on by trying to get the value like this.

    roomPushKey.once('child_added').then(function(dataSnapshot) {
        let snapVal = dataSnapshot.val();
        console.log(snapVal);
});

Question 2 (which I think is basically question 1 rephrased): How can I get the snapVal outside the then. method's scope?

    return change.after.ref.parent.parent.parent.child('/rooms')
.child(snapVal).child('/ins').set(afterData);
      // snapVal should go above
   });

Error message: ReferenceError: snapVal is not defined

Answer 1

The following should work.

const admin = require("firebase-admin");
....
....

exports.updateRoom = functions.database.ref('/doors/{MACaddress}').onWrite((change, context) => {
    const afterData = change.after.val(); // data after the write

    const roomPushKey = afterData.inRoom;
    const ins = afterData.ins;

    const updates = {};
    updates['/rooms/' + roomPushKey] = ins;
    return admin.database().ref().update(updates);

}).catch(error => {
    console.log(error);
    //+ other rerror treatment if necessary

});

Here are some explanations:

You get the roomPushKey by reading the "data after the write" as an object: roomPushKey = afterData.inRoom. You don't need to do roomPushKey.once('child_added').then()

Once you have the roomPushKey, you create a new child node in the rooms node by using update() and creating an object with square brackets notation which allow you to assign the id of the node (i.e. roomPushKey).

Note that you could also do:

return admin.database().ref('/rooms/' + roomPushKey).set(ins);

Note also that you have to import firebase-admin in order to be able to do return admin.database().ref()...

Finally, I would suggest that you have a look at the three following videos from the Firebase team: youtube.com/watch?v=7IkUgCLr5oA&t=517s & youtube.com/watch?v=652XeeKNHSk&t=27s & youtube.com/watch?v=d9GrysWH1Lc. A must for anyone starting coding for Cloud Functions.