更新索引值时，Firestore addSnapshotListener 无法收听文档更新

Question

I am not quite sure if I am doing this correctly in Firebase in Swift. Say I store some date in a collection called "temp", and I am trying to listen to any update on the document. Each document has couple fields. For instance, one field is userId, and another one is updateTs. In order to query the most recent documents, my listener is like this

messageListener = Firestore.firestore().collection("temp")
                .whereField("userId", isEqualTo: "\(userId)")
                .whereField("updateTs", isLessThan: lastUpdateTs)
                .order(by: "updateTs", descending: true)
                .limit(to: 20)
                .addSnapshotListener { querySnapshot, error in
                    guard let snapshot = querySnapshot else {
                        return
                    }
                    for i in 0..<snapshot.documentChanges.count {
                        var change = snapshot.documentChanges[i]
                        // do things herer
                        if (change.type == .added) { print("added") }
                        if (change.type == .removed) { print("removed") }
                        if (change.type == .modified) { print("modified") }
                    }
                }

Since I am querying using both whereField and order, i have to create an composite index (userId + updateTs).

Everything works well with the initial launch, however, when I try to update the values on the updateTs field while the userId field is unchanged using

let messageData: [String: Any] = ["userId": userId, "updateTs": updateTs]
Firestore.firestore().collection("temp").document(thisDocument).updateData(messageData)

The above listener identifies the above change as removed instead of modified , and after the first time the listener observes the change, it will no longer be able to observe the change any more(probably due to it was identified as removed )

My hypothesis is that it is because I am updating the value for an index, which causes this issue. In this case, is there any workaround? Any help is appreciated

Answer 1

What is the value of updateTs that you set on the document?

My guess is that you're setting updateTs to va value larger than lastUpdateTs . In that case the updated document no longer matches your query, and is removed from the query results. So that would mean change.type is .removed as the document was removed from the query results.