HTTP function return initial array values

Question

I've got this firebase cloud function that I've coded to count the number of registered users vs the anynymous users.

// Recalc totals user 
exports.recalcTotalUsers = functions.https.onRequest((req, res) => {
    var arr = {
        anonymous: 0,
        registered: 0
    };

    console.log('starting recalcTotalUsers');
    admin.database().ref("users").once("value").then((snapshot) => {
        snapshot.forEach(function (uid) {
            if (uid.child('/email').val() == ANONYMOUS_STRING) {
                arr.anonymous++;
            } else {
                arr.registered++;
            }
            console.log(`1. ${arr.anonymous}:${arr.registered}`)
        })
    });
    res.status(200).send(`ok registered: ${arr.registered}, anonymous: ${arr.anonymous}`)  
 });

When the function returns I get alway anonymous = 0 and registered = 0 event if they have different values... what I am doing wrong?

creativecreatorormaybenot · Accepted Answer · 2018-02-16 08:25:13Z

You have to move your response! Because at the moment, let's look at your code:

admin.database().ref("users").once("value").then((snapshot) => {
    snapshot.forEach(function (uid) {
        if (uid.child('/email').val() == ANONYMOUS_STRING) {
            arr.anonymous++;
        } else {
            arr.registered++;
        }
        console.log(`1. ${arr.anonymous}:${arr.registered}`)
    })
});
res.status(200).send(`ok registered: ${arr.registered}, anonymous: ${arr.anonymous}`)

As you might know, the database functions are all asynchronous, which means that they

take time to be executed
have promises and thus do not wait before the next line of code is executed

res.status(200).send(ok registered: ${arr.registered}, anonymous: ${arr.anonymous})

That line is executed before you query through your "users" snapshot. You have to move it, and best practice would be another promises (.then(...)), but you can just do it like this:

admin.database().ref("users").once("value").then((snapshot) => {
    snapshot.forEach(function (uid) {
        if (uid.child('/email').val() == ANONYMOUS_STRING) {
            arr.anonymous++;
        } else {
            arr.registered++;
        }
        console.log(`1. ${arr.anonymous}:${arr.registered}`)
    })
    res.status(200).send(`ok registered: ${arr.registered}, anonymous: ${arr.anonymous}`)
});

Doug Stevenson · Accepted Answer · 2018-02-16 08:26:25Z

The database query is asynchronous and does not finish immediately. You need to use the promise return by admin.database().ref("users").once() to wait for the result of the query, and only send the response to the client after it succeeds. Currently, your response is sent to the client before the query completes.

Instead, put the response to the client inside the callback to the promise from once(), not outside:

admin.database().ref("users").once("value").then((snapshot) => {
    snapshot.forEach(function (uid) {
        if (uid.child('/email').val() == ANONYMOUS_STRING) {
            arr.anonymous++;
        } else {
            arr.registered++;
        }
        console.log(`1. ${arr.anonymous}:${arr.registered}`)
    })
    res.status(200).send(`ok registered: ${arr.registered}, anonymous: ${arr.anonymous}`)  
});

Please read more about Firebase asynchronous APIs.

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