为什么我不能得到所有文件存储在firestore子集合？

Question

    func getAttendedEventsFromBeginning(completion: @escaping (_ eventID: [String]?,QueryDocumentSnapshot?)->Void) {

        FirestoreDocumentReference.users(uidUser: uid).reference().collection("attendedEvents")
            .getDocuments { (snapshot, error) in

                let lastDocument = snapshot?.documents.last

                if let error = error {
                    completion(nil,lastDocument)
                    print("Error when fetching attended events documents in user subcollection: \(error.localizedDescription)")
                } else {
                    print("Successfully fetching attended events documents in user subcollection from Firestore ")

                    guard let documentsSnapshot = snapshot else {
                        completion(nil,lastDocument)
                        return
                    }

                    let eventDocuments = documentsSnapshot.documents
                    print("xxxxx")
                    print(eventDocuments)

                    var attendedeventIDs = [String]()

                    for document in eventDocuments {
                        let eventDictionary = document.data()
                        let theEvent = eventDictionary["eventID"] as! String
                        attendedeventIDs.append(theEvent)
                    }

                    print(attendedeventIDs)

                    completion(attendedeventIDs,lastDocument)
                }
            }
    }

但是如果我从模拟器中删除应用程序并重新安装，我得到了所有的三个数据。是缓存还是什么？