Swift:Firestore子集合、自定义对象和侦听器

我有一个模型模式,如下图所示。

Countries 以及相关数据。我已经创建了各自的结构,我的想法是使用链接中显示的自定义对象方法 Custom_Objects . 现在我的问题是 subcollections 我不会进来的 querysnapshot (我只获取字段),因此我无法进行直接对象映射(因为我必须查询和检索子集合才能使对象完整)。例如: Country States 作为属性之一,不带状态 国 州 还有其他省份。现在我正在做递归循环来构建整个结构,我感觉不太好。

所以我的问题是,处理此类数据的最佳方式是什么(前提是没有标准化的空间,我们无法避免子集合)?

另外,如果我想得到有关州、省或镇的任何更改的通知,我是否需要分别向每个集合添加侦听器,或者向根目录添加侦听器就足够了?

    db.collection("countries").getDocuments { (QuerySnapshot, error) in
    if let error = error {
        print("\(error.localizedDescription)")
    }else{
        var docCount = QuerySnapshot!.documents.count
        for document in QuerySnapshot!.documents {
            self.fetchStatesForDoc(document: document, completion: { (nodes) in
                var data = document.data()
                data["states"] = nodes
                let country = Country(dictionary: data)
                self.countryList.append(country!)
                print(self.sectionList)
                docCount = docCount - 1
                if docCount == 0{
                    DispatchQueue.main.async {
                        self.countryCollection.reloadData()
                    }
                }
            })
        }
    }
}
}
func fetchStatesForDoc(document: DocumentSnapshot, completion:@escaping ([State])-> Void){

    var states = [State]()
    document.reference.collection("states").getDocuments(completion: { (QuerySnapshot, error) in
        if let error = error {
            print("\(error.localizedDescription)")
        }else{
            var docCount = QuerySnapshot!.documents.count
            for document in QuerySnapshot!.documents {
                //print("\(document.documentID) => \(document.data())")
                var data = document.data()
                self.fetchProvincesForDoc(document: document, completion: { (provinces) in
                    data["Provinces"] = provinces
                    let state = State(dictionary: data)
                    states.append(state!)
                    docCount = docCount - 1
                    if docCount == 0{
                        completion(state)
                    }
                })
            }
        }
    })
}
func fetchProvincesForDoc(document: DocumentSnapshot, completion:@escaping ([Province])-> Void){

    var provinces = [Province]()
    document.reference.collection("provinces").getDocuments(completion: { (QuerySnapshot, error) in
        if let error = error {
            print("\(error.localizedDescription)")
        }else{
            var docCount = QuerySnapshot!.documents.count
            for document in QuerySnapshot!.documents {
                //print("\(document.documentID) => \(document.data())")
                var data = document.data()
                self.fetchTownsForDoc(document: document, completion: { (towns) in
                    data["towns"] = provinces
                    let province = Province(dictionary: data)
                    provinces.append(province!)
                    docCount = docCount - 1
                    if docCount == 0{
                        completion(province)
                    }
                })
            }
        }
    })
}
func fetchTownssForDoc(document: DocumentSnapshot, completion:@escaping ([Towns])-> Void) {

    var towns = [Towns]()
    document.reference.collection("towns").getDocuments(completion: { (QuerySnapshot, error) in
        if let error = error {
            print("\(error.localizedDescription)")
        }else{
            for document in QuerySnapshot!.documents {
                //print("\(document.documentID) => \(document.data())")
            }
            towns = QuerySnapshot!.documents.compactMap({Towns(dictionary: $0.data())})
            completion(towns)
        }
    })
}