Firebase 云函数。 无法读取未定义 (.ref) 的属性父级

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.

Answer 1

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 ischange which contains before and after which are of type DocumentSnapshot , it is those properties you should be using eg change.after.ref .