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I'm working on a web application that will visualize data from my Firebase database. But first, I want to be able to "count" the total number of users with a given data so that I can then use that count number in my graphs.

For reference, my database looks like this:

Because I expect separate totals for the required keys, I'm guessing that I'll need separate counters for each one. I've started writing a cloud function to keep track of when a new user is created:

import * as functions from 'firebase-functions'

export const onMessageCreate = functions.database

.ref('/students/{studentID}')

.onCreate((snapshot, context) => {

    const userData = snapshot.val()



    const afterGrad = userData.afterGrad

    const gender = userData.gender

    const gradDate = userData.gradDate

    const program = userData.program

    const race = userData.race

    const timeToComplete = userData.timeToComplete

})

But now, I'm extremely lost at how I should go about creating counters. Would something like this suffice, with an individual counter for each constant?

import * as functions from 'firebase-functions'

var counterAfterGrad; 



export const onMessageCreate = functions.database

.ref('/students/{studentID}')

.onCreate((snapshot, context) => {

    const userData = snapshot.val()

    const afterGrad = userData.afterGrad

    var counterAfterGrad++

})

Or should I be thinking about using a transaction in this case? I'm really not sure of the best way, and would really appreciate some help.

Yes, you should use a transaction. See the documentation here: https://firebase.google.com/docs/database/web/read-and-write#save_data_as_transactions and https://firebase.google.com/docs/reference/js/firebase.database.Reference#transaction

For counting the overall number of users you could do as follows:

export const onMessageCreate = functions.database

.ref('/students/{studentID}')

.onCreate((snapshot, context) => {

    const userData = snapshot.val()

    const afterGrad = userData.afterGrad



    const allUsersCounterRef = admin

      .database()

      .ref('allUsersCounter');



    return allUsersCounterRef

      .transaction(counter_value => {

        return (counter_value || 0) + 1;

      })



})

Note that you may have to take into consideration the deletion of a user.

You could very well have several counters, for example by "gender" (male/female) and by "program". You would then use an object in the transaction as follows:

exports.onMessageCreate = functions.database

  .ref('/students/{studentID}')

  .onCreate((snapshot, context) => {

    const userData = snapshot.val();



    const countersRef = admin.database().ref('counters');



    return countersRef.transaction(currentData => {

       currentData[userData.gender] = (currentData[userData.gender] || 0) + 1;

       currentData[userData.program] = (currentData[userData.program] || 0) + 1;

       return currentData;

    });

  });