Firebase functions - Counting children and updating an entry

I have been trying to use Firebase Functions to write a simple method, but I am unfamiliar with JS.

Below is the structure of my Realtime Database

-spots

---is_hidden: false

---likes

------like_id_1: true

---dislikes

------dislike_id_1: true

I am trying to write a simple method that does the following: Whenever an entry is added to dislikes, count the likes and the dislikes.

If the number of dislikes is larger than the number of ( likes + 5 ),
change the value of is_hidden to true

This is my attempt to solving the problem

exports.checkHiddenStatus = functions.database.ref('/spots/{spotid}').onWrite(
(change, context) => {
const collectionRef = change.after.ref;
const isHiddenRef = collectionRef.child('is_hidden');
const likesRef = collectionRef.child('likes');
const dislikesRef = collectionRef.child('dislikes');


if(isHiddenRef.before.val()) return;

let likeCount = likesRef.numChildren();
let dislikeCount = dislikesRef.numChildren();

let isHidden = false;

if( dislikeCount >= (likeCount + 5))
isHidden = true;

if(!isHidden) return;

// Return the promise from countRef.transaction() so our function
// waits for this async event to complete before it exits.
return isHiddenRef.transaction((current) => {
return isHidden;
}).then(() => {
return console.log('Counter updated.');
});
});


Sadly, because I have no experience with JS I keep getting stuck with error messages I don't understand. The most recent being

TypeError: Cannot read property 'val' of undefined
at exports.checkHiddenStatus.functions.database.ref.onWrite (/user_code/index.js:28:28)

Can somebody please help me write this function? Thank you!

1 Answer
1

It looks like you're trying to treat a database Reference object like a Change object. Change has before and after properties, but a reference does not.

before

after

If you have a database reference object, and you want the value of the database at that location, you need to query it with its once() method.

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