Firebase Cloud Functions. Cannot read property parent of undefined (.ref)

Question

I am trying to deploy the following function to firebase. The function deploys fine, but when the function triggers I get an error: cannot read property 'parent' of undefined. The error occurs in the first line I reference parent. I used console.log on snapshot and snapshot.ref, and although snapshot exists, snapshot.ref is undefined.

I have used snapshot.ref.parent in other cloud functions and it is working fine. There are two main difference with this function: (a) it is an onUpdate (I have previously been using onCreate and onDelete) (b) it is an async function.

exports.likeRating = functions.database.ref('Ocean/{waveId}/Likes').onUpdate(async (snapshot) =>{
    let likes; let dislikes; let comments; let echoes;

    await snapshot.ref.parent.child('Dislikes').once('value').then(response=>{dislikes = response.val(); return null});
    await snapshot.ref.parent.child('Likes').once('value').then(response=>{likes = response.val(); return null});
    await snapshot.ref.parent.child('Comments').child('CommentsCount').once('value').then(response=>{comments = response.val(); return null});
    await snapshot.ref.parent.child('Echoes').once('value').then(response=>{echoes = response.val(); return null});

    snapshot.ref.parent.child('Rating').set(dislikes+likes+comments+echoes);
    return null;

}

Any ideas as to why I am getting this error? All help is appreciated.

Dominic Dominic · Accepted Answer · 2019-09-26T13:42:09

That function will run significantly slower than it needs to as you're waiting for your requests in series, you should await a Promise.all([<Promises>]) instead, also the return null is redundant.

I'm also not sure why you add everything up each time instead of incrementing the Rating value but maybe I didn't think about it as much as you.

If you look at the docs the signature of the callback is function(non-null functions.Change containing non-null functions.firestore.DocumentSnapshot, optional non-null functions.EventContext)

So the first param is change which contains before and after which are of type DocumentSnapshot, it is those properties you should be using e.g. change.after.ref.

Firebase Cloud Functions. Cannot read property parent of undefined (.ref)

1 Answers