How to Count Users with a Firebase Cloud Function (getting Function Returned Undefined error)

Question

I have a Firebase Cloud Function that assigns a number to a user on onWrite. The following code works but something is wrong because the console logs state Function returned undefined, expected Promise or value.

I'm also not sure how to refer to the root from inside the onWrite so I've created several "parent" entries that refer to each other. I'm sure there is a better way.

onWrite triggers on this:

/users/{uid}/username

The trigger counts the children in /usernumbers and then writes an entry here with the uid and the child count + 1:

/usernumbers/uoNEKjUDikJlkpLm6n0IPm7x8Zf1 : 5

Cloud Function:

'use strict';

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.setCount = functions.database.ref('/users/{uid}/username').onWrite((change, context) => {
    const uid = context.params.uid;
    const parent1 = change.after.ref.parent; //uid
    const parent2 = parent1.ref.parent;      //users
    const parent3usernumbers = parent2.ref.parent.child('/usernumbers/');
    const parent3usernumbersuid = parent2.ref.parent.child('/usernumbers/'+uid);

    parent3usernumbers.once("value")
       .then(function(snapshot) {
       var a = snapshot.numChildren();
       return parent3usernumbersuid.transaction((current) => {
          return (a + 1);
       }).then(() => {
          return console.log('User Number Written', uid, a);
       });
    });
});

Is there a better way to do this? How can I get the Function Returned Undefined error to go away?

I should also mention it takes a few seconds for the 'usernumber' entry to be written. I'm guessing it's waiting for the function to return something.

diouze diouze · Accepted Answer · 2018-08-21T16:02:19

Your function have to return a Promise :

exports.setCount = functions.database.ref('/users/{uid}/username').onWrite((change, context) => {
    const uid = context.params.uid;
    const parent1 = change.after.ref.parent; //uid
    const parent2 = parent1.ref.parent;      //users
    const parent3usernumbers = parent2.ref.parent.child('/usernumbers/');
    const parent3usernumbersuid = parent2.ref.parent.child('/usernumbers/'+uid);

    return new Promise((resolve, reject) => {
        parent3usernumbers.once("value").then(function(snapshot) {
           var a = snapshot.numChildren();
           return parent3usernumbersuid.transaction((current) => {
               return (a + 1);
            }).then(() => {
               console.log('User Number Written', uid, a);
               resolve({uid : uid, a : a})
            }).catch(function(e) {
               reject(e)
            })
        });
    });
});

How to Count Users with a Firebase Cloud Function (getting Function Returned Undefined error)

1 Answers