How do I properly grab the users profile from Realtime Database to get their username before the cloud function returns? - firebase

Question

I am implementing Cloud Functions to send my users notifications for when interesting things happen like following, liking, commenting. I have copied & adapted the Firebase tutorial for sending a notification when a change at the followers node is detected, but I need to also query the database to get the follower's account data including their username. I think I am close, but the function doesn't finish in time and I'm having trouble understanding promises. Here is the function:
exports.sendFollowerNotification = functions.database.ref(`/userFollowers/{followedUid}/{followerUid}`)
.onWrite((change, context) => {
const followerUid = context.params.followerUid;
const followedUid = context.params.followedUid;
// If un-follow we exit the function
if (!change.after.val()) {
return console.log('User ', followerUid, 'un-followed user', followedUid);
}
console.log('We have a new follower UID:', followerUid, 'for user:', followedUid);
// Get the list of device notification tokens.
const getDeviceTokensPromise = admin.database()
.ref(`/users/${followedUid}/notificationTokens`).once('value');
console.log('Found the followed user\'s token')
const userInfo = admin.database().ref(`/users/${followedUid}`).once('value');
console.log(userInfo)
const username = userInfo['username'];
console.log(username);
////////////////// ABOVE is where I'm trying to get the username by reading their account data ///////////////////
// Get the follower profile.
const getFollowerProfilePromise = admin.auth().getUser(followerUid);
// The snapshot to the user's tokens.
let tokensSnapshot;
// The array containing all the user's tokens.
let tokens;
return Promise.all([getDeviceTokensPromise, getFollowerProfilePromise]).then(results => {
tokensSnapshot = results[0];
const follower = results[1];
// Check if there are any device tokens.
if (!tokensSnapshot.hasChildren()) {
return console.log('There are no notification tokens to send to.');
}
console.log('There are', tokensSnapshot.numChildren(), 'tokens to send notifications to.');
console.log('Fetched follower profile', follower);
// Notification details.
const payload = {
notification: {
title: 'You have a new follower!',
body: `{username} is now following you.`,
}
};
// Listing all tokens as an array.
tokens = Object.keys(tokensSnapshot.val());
// Send notifications to all tokens.
return admin.messaging().sendToDevice(tokens, payload);
}).then((response) => {
// For each message check if there was an error.
const tokensToRemove = [];
response.results.forEach((result, index) => {
const error = result.error;
if (error) {
console.error('Failure sending notification to', tokens[index], error);
// Cleanup the tokens who are not registered anymore.
if (error.code === 'messaging/invalid-registration-token' ||
error.code === 'messaging/registration-token-not-registered') {
tokensToRemove.push(tokensSnapshot.ref.child(tokens[index]).remove());
}
}
});
return Promise.all(tokensToRemove);
});
});
How can I ensure that username will have been made available before it returns? Thanks.

Answer 1

Ok, I think I get what you are saying...
These lines of code don't do what you think. All DB reads are done asynchronous, so...
const userInfo = admin.database().ref(`/users/${followedUid}`).once('value');
console.log(userInfo)
const username = userInfo['username'];
console.log(username);
once returns a promise, so userInfo is actually a promise to return the data. You won't get the data until you do a then.
More chaining promises I'm afraid... just rename userInfo to userInfoPromise and add it to your Promise.All array.