Question

i have function i am using to do updates to my databased based on Cron Job. It looks like this ( worth saying i had a lot of help here )

exports.minute_job =
  functions.pubsub.topic('minute-tick').onPublish((event) => { 

    var ref = admin.database().ref("comments")
    ref.once("value").then((snapshot) => {
        var updates = {};
        snapshot.forEach(commentSnapshot => {
            var comment = commentSnapshot.val();

            var currentRating = comment.rating - comment.lastRating;          
            var newScore = ((Math.abs(comment.internalScore) * 0.95) + currentRating) * -1;

            if(newScore < 0.000001) { newScore = 0.000001}

            updates[commentSnapshot.key + "/lastRating"] = comment.rating;
            updates[commentSnapshot.key + "/internalScore"] = newScore;         
        });

        ref.update(updates);
    })
  });

Its all working perfectly, except i am getting this warning from Firebase logs:

"Function returned undefined, expected Promise or value"

Thanks for any help

Answer 1

Since your Cloud Function doesn't return a value, the Google Cloud Functions engine contain doesn't know when the code is finished. In many cases this means that GCF will simply terminate the contain of your function right after the closing }) has executed. But at that point, your code is likely still loading data from the database, and it definitely hasn't update the database yet.

The solution is to return a promise, which is just an object that will signal when you're done with the database. The good news is that both once() and update() already return promises, so you can just return those:

exports.minute_job =
  functions.pubsub.topic('minute-tick').onPublish((event) => { 

    var ref = admin.database().ref("comments")
    return ref.once("value").then((snapshot) => {
        var updates = {};
        snapshot.forEach(commentSnapshot => {
            var comment = commentSnapshot.val();

            var currentRating = comment.rating - comment.lastRating;          
            var newScore = ((Math.abs(comment.internalScore) * 0.95) + currentRating) * -1;

            if(newScore < 0.000001) { newScore = 0.000001}

            updates[commentSnapshot.key + "/lastRating"] = comment.rating;
            updates[commentSnapshot.key + "/internalScore"] = newScore;         
        });

        return ref.update(updates);
    })
  });

Now Google Cloud Functions know that your code is still working after the }), because you returned a promise. And then when your update() is done, it resolves the promise it return and Google Cloud Functions can close the container (or at the very least: stop charging you for its usage).

Firebase Cloud Function Cron Update

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