CODEWITHSUNDEEP
javascriptfirebasefirebase-realtime-databasegoogle-cloud-functions
manic
manic

Reputation: 83

Firebase functions: Listen to all delete changes

I have a database like this:

- users
    - userId1
        - activities
            - football: "20€"
        - competitions
            - competitionId1
                - football
                    - prize: "40€"

    - userId2
        - activities
            - baskets: "20€"
            - football: "30€"
        - competitions
            - competitionId4
                - basket
                    - prize: "40€"

So I would like to be notified on all deletes on this, I tried to use

functions.database.ref("users/{userId}").onDelete();

But it only listens to users/{userId}, I could use .onUpdate(), but I really need to know the entire path of the deleted object.

The only thing I could try to do is using .onUpdate() and doing a deep comparison between the old and the new value to retrieve what element got removed.

But I don't think it's the best solution

For example:

If I remove users/userId1/competitions

I will be notified that users/userId1/competitions is removed

Upvotes: 1

Views: 392

Answers (2)

Renaud Tarnec
Renaud Tarnec

Reputation: 83093

Have a look at this section in the doc for Cloud Functions triggered by Realtime Database events.

Path specifications match all writes that touch a path, including writes that happen anywhere below it.

...

If the event data might be large, consider using multiple functions at deeper paths instead of a single function near the root of your database. For the best performance, only request data at the deepest level possible.

It's really up to you to decide if you should defined several Cloud Functions. However, since you want to listen to deletions, it will be probably easier to write a Cloud Function for each level, like:

functions.database.ref("users/{userId}").onDelete(...);

functions.database.ref("users/{userId}/{activitiesOrCompetitions}").onDelete(...);

functions.database.ref("users/{userId}/{activitiesOrCompetitions}/{CompetitionId}").onDelete(...);

Note that each time you'll delete a CompetitionId node, if there is no more competitions for this user, you'll trigger the second Cloud Function above.

Again, it's up to you to decide if you want to trigger several Cloud Functions for one deletion or you prefer to trigger only one Cloud Function (with onUpdate()) and compare the snapshots, as you mentioned in your question. Remember that there is a generous free tier for Cloud Functions executions of 2M/month.

Upvotes: 1

Tarik Huber
Tarik Huber

Reputation: 7388

Have you tried changing the listener to:

functions.database.ref("users/{userId}/{path}").onDelete();

Then path in your context would be either "activities", "competitions" etc..

Upvotes: 0

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