CODEWITHSUNDEEP
javascriptfirebasegoogle-cloud-functions
Laurent Maquet
Laurent Maquet

Reputation: 400

Add exceptions on firebase cloud functions triggers

In a social app, I have a cloud function that updates a 'likes' counter whenever a post is liked, which is to say whenever the following reference is updated:

/likes/{postId}/{userid}

'countOfLikes' is written at the same level of the wildcard {userId} :

exports.countLikeChange = functions.database.ref('/likes/{postId}/{userid}').onWrite(event => {
    const collectionRef = event.data.ref.parent;
    var counterRef = collectionRef.child('countOfLikes');


    return collectionRef.once('value').then(messagesData => counterRef.set(messagesData.numChildren() - 1));
});

With my current code, when a user like a post, the function is triggered first to update countOfLike, which in turn trigger the same function to do the same action...

Is there a way to specify an exclusion so that the function will not be triggered if {userId} == 'countOfLikes' ?

I know that I could use onCreate instead of onWrite, but you must know that in my app, one user could also remove his 'like'.

Upvotes: 0

Views: 109

Answers (1)

Frank van Puffelen
Frank van Puffelen

Reputation: 598623

There is no way to exclude a specific child from triggering a function.

If you find that need, it typically means you've combined types of data that should be kept separate.

For example, I would expect your like counts to be in a separate node altogether, e.g. /likeCounts/$postId. If you structure it like that, updating the count for a new like won't retrigger the function.

Upvotes: 2

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