Prevent firestore onUpdate cloud functions when onSnapshot is used

October 16, 2023

I got a question to onSnapshot and cloud functions behaviour.

If I use onSnapshot, as far as I understand, it does most locally and then updates with the cloud every like 1 sec with a hook.
But I have a cloud function functions.firestore.document(…).onUpdate and this one will be called every time of those update hooks if I have like a text field. The function itself is there to check if a type field (typeA,typeB) has been changed, and if so it does some stuff in other collections.

can I trigger the function somehow manually, like when the subsription is unsubsribed for example, that would be the best? but then I cant compare using the snap.before/after functionality in the cloud functions?

what would be a good way to handle this?

Here is my cloud function, it updates the parent document if the type field is changed in the updated document. And I don’t want to have tons of invocations on OnSnapshot updates

export const incrementCountsOnUpdate = functions.firestore
  .document('parent/{parentId}/chiild/{chiildId}')
  .onUpdate(async (snap, context) => {
    const beforeType = snap.before.data().type
    const afterType = snap.after.data().type
    if (beforeType === afterType) return
    const setRef = snap.before.ref.parent.parent
    if (setRef) {
      await setRef.update({
        [getCounter(beforeType)]: FieldValue.increment(-1),
        [getCounter(afterType)]: FieldValue.increment(1)
      })
    }
  })