firebase functions showing error cannot read property previous of undefined

Question

I had implemented firebase functions in my app and previously it was working fine but now it is showing error Cannot read property \'previous\' of undefined

Answer 1

The signature of Cloud Functions triggers has changed. You seem to be using beta, but are deploying to the latest version. See the migration guide for complete instructions.

From there:

Before (<= v0.9.1)

exports.dbWrite = functions.database.ref('/path').onWrite((event) => {
  const beforeData = event.data.previous.val(); // data before the write
  const afterData = event.data.val(); // data after the write
});

Now (>= v1.0.0)

exports.dbWrite = functions.database.ref('/path').onWrite((change, context) => {
  const beforeData = change.before.val(); // data before the write
  const afterData = change.after.val(); // data after the write
});

So your code should look something like this:

exports.LoveNotification = functions.database.ref("/Member/{pushId}").onWrite((change, context) => {

 if (change.before.exists()) {
    return;
 } else {
    var eventLove = change.after.data.val();
    var author =eventLove.fullname;
    var title = eventLove.course;
    var key = eventLove.key;

    const payload = {
        "data": {
                    "post_id": key
                  },
        notification: {
            title: author +'Joined the app',
            body: `Course `+title,
            sound: "default",
            icon: "ic_launcher",

        }
    };

    const options = {
        priority: "high",
        timeToLive: 60 * 60 * 24 //24 hours
    };
    console.log('Sending notifications');
    return admin.messaging().sendToTopic("Member", payload, options);

    }
});