Firebase cloud function finished before complete the foreach

Question

I want to update the list of "Reservations" with some new variables. But I can't make it work because the function ends before updating. I know the problem is because I make asynchronous calls but I can't solve it. How can I use Promise in this case?

I edited the code using Promise but still does not update the "Reservations" Returns {"data": null} to my website console In the firebase console does not generate any errors. Return the message "reservations actualized"

exports.actualizeReservations = functions.https.onCall((data, response) => {
var promisesUpdateReservations = [];
return admin.database().ref(Constants.RESERVATIONS).once("value")
.then((snapshot) => {
    console.log("RESERVATIONS: " + snapshot)
    snapshot.forEach((reserveSnap) => {
        var reserve = reserveSnap.val();
        if(reserve.reservationId && reserve.restoId) {
            admin.database().ref(`${Constants.RESTAURANTS}/${reserve.restoId}`).once("value")
            .then((restoSnap) => {
                if(restoSnap.exists() && restoSnap.val() !== null) {
                    var resto = restoSnap.val();
                    if(resto.address && !resto.address.fullAddress) {
                        var restoAddress = resto.address ? {
                            street: resto.address.street ? resto.address.street : "",
                            fullAddress: resto.address.fullAddress ? resto.address.fullAddress : "",
                            city: resto.address.city ? resto.address.city : "",
                            country: resto.address.country ? resto.address.country : "",
                            postalCode: resto.address.postalCode ? resto.address.postalCode : "",
                            province: resto.address.province ? resto.address.province : "",
                            l: resto.l ? resto.l : null,
                            g: resto.g ? resto.g : null,
                        } : null;
                        var restoUserIDs = `${reserve.restoId}/${reserve.userId}`;
                        const promiseUpdateReservation = admin.database().ref(`${Constants.RESERVATIONS}/${reserve.reservationId}`).update({
                            restoAddress,
                            restoUserIDs
                        })
                        promisesUpdateReservations.push(promiseUpdateReservation)
                    }
                }
            })
            .catch((err) => {
                console.log("resto not found")
            });
        }
    });
    Promise.all(promisesUpdateReservations)
    .then(() => {
        console.log("reservations actualized");
        return { code: 0, result: "successful", description: "reservations actualized" };
    })
})
.catch((err) => {
    console.log("get restaurants error: " + err);
    return { code: 1, result: "successful", description: "reservations not loaded" };;
});
})

Answer 1

This function is going to complete immediately every time it's invoke, and likely perform none of its work. This is because it's not returning anything at all from the top-level function callback. Instead, you need to return a promise from the top level of the function that resolves with the data to send to the client only after all the async work is complete (and you're kicking off a lot of it here). Proper handling of promises is critical to making Cloud Functions work correctly.