Firestore Cloud Function Query returning value after database query?

Question

Currently, I am querying for objects in the database to update. A snippet of the function that does so is

 return getPostsForDate.get().then(snapshot => {
        const updates = {}
        var counter = 0
        const batch = admin.firestore().batch()
        snapshot.forEach((doc) => {

            var key = doc.id
            return admin.database().ref('/convoID/' + key).once('value', (snapshot) => {
                if (snapshot.exists()) {
                    const convoIDCollection = snapshot.val()
                    for (var child in convoIDCollection) {

                        console.log(child)
                        updates["conversations/" + child] = null
                        updates["messages/"+ child] = null
                        updates["convoID/"+ child] = null
                    }
                }
                updates["/convoID/" + key] = null
                updates["/reveals/" + key] = null
                updates["/postDetails/" + key] = null
                const postFireStoreRef = admin.firestore().collection('posts').doc(key)
                const posterRef = admin.firestore().collection('posters').doc(key)
                batch.delete(postFireStoreRef)
                batch.delete(posterRef)
                counter++
                console.log(counter)
             })

        })
        if (counter > 0) {
            console.log("at the deletion point")
              return Promise.all[admin.database().ref().update(updates), batch.commit()] 
        }
        else {
            console.log("null")
            return null
        }
})

Essentially, after the firestore queries for the posts, additional details are received from the realtime database and added to an array. Finally, I commit all these updates through a promise. However, the function that returns the updates is never reached - in order to ensure that updates are needed to the database, I have a counter that counts the number of updates. If it is greater than 0, I return

 return Promise.all[admin.database().ref().update(updates), batch.commit()]

However, it seems like the return function is executed before the additional details are received, as it keeps on returning "null" to the console log which should only happen if the counter is less than 0.

Essentially, how do I wait for the data to be queried before executing the updates?

Update

    return getPostsForDate.get().then(snapshot => {
    const updates = {} 
    const promises = []
    var counter = 0
    const batch = admin.firestore().batch()
    snapshot.forEach((doc) => {
 promises.push (
        admin.database().ref('/convoID/' + key).once('value', (snapshot) => {
            if (snapshot.exists()) {
                const convoIDCollection = snapshot.val()
                for (var child in convoIDCollection) {
                    updates["conversations/" + child] = null
                    updates["messages/"+ child] = null
                    updates["convoID/"+ child] = null
                }
            }
            updates["/convoID/" + key] = null
            updates["/reveals/" + key] = null
            updates["/postDetails/" + key] = null
            const postFireStoreRef = admin.firestore().collection('posts').doc(key)
            const posterRef = admin.firestore().collection('posters').doc(key)
            batch.delete(postFireStoreRef)
            batch.delete(posterRef)
            counter++
         })
        )
    })
    Promise.all(promises).then(() => {
    if (counter > 0) {
        console.log("at the deletion")
          return Promise.all[admin.database().ref().update(updates), batch.commit()] 
    }
    else {
        console.log("null")
        return null
    }
})
})
})

Answer 1

admin.database().ref('/convoID/' + key).once(...) is asynchronous and returns a promise, but your code isn't using those promises to wait for each query to complete. This means your code is moving on to the if/else immediately after the snapshot iteration, but before counter is ever updated, or the batches are added.

You'll need to restructure your code to collect all those promises from once() into an array, use Promise.all() to wait for all those promises to resolve, then commit the batch.