使用完成处理程序对 Firestore 集合进行顺序查询

Question

我正在通过下面的主要功能查询餐厅列表。然后我使用餐馆列表从另一个集合中获取他们的膳食计划列表：

MealplanCalls.getRestaurants(userId: userId) { (restaurantList, error) in
            if let error = error {
                self.showError(show: "Error", display: error)
            } else {
                var currentPlansArray = [Mealplan]()
                var restaurantIndex = 0
                while (restaurantIndex < restaurantList.count) {
                    MealplanCalls.getPlans(restaurantId: restaurantList[restaurantIndex]) { (mealplans, error) in
                        guard let mealplans = mealplans, mealplans.count > 0 else { return }
                        self.planArray.append(contentsOf: mealplans)
                        print("empty : \(self.planArray.count), \(self.planArray)")
                        if let error = error {
                            self.showError(show: "Error", display: error)
                        }
                        DispatchQueue.main.async {
                            self.planTable.reloadData()
                        }
                    currentPlansArray.removeAll()
                    restaurantIndex += 1
}
            }
        }

这是我获取餐厅列表的服务：

static func getRestaurants(userId : String, completionHandler : @escaping ([String], String?) -> Swift.Void) {
        let db = Firestore.firestore().collection("Restaurant_Data")
        var restaurantList = [String]()
        db.whereField("users", arrayContains: userId).getDocuments { (restaurantSnapshot, error) in
            if let error = error {
                completionHandler([], error.localizedDescription)
            } else {
                for document in restaurantSnapshot!.documents {
                    restaurantList.append(document.documentID)
                }
                completionHandler(restaurantList, nil)
            }
        }
    }

这是我获取膳食计划的地方：

static func getPlans(restaurantId : String, completion : @escaping ([Mealplan]?, String?) -> Void) {
        let db = Firestore.firestore().collection("Meal_Plans")
        db.whereField("restaurantId", isEqualTo: restaurantId).order(by: "hour", descending: false).getDocuments { (querySnapshot, error) in
            if let error = error {
                completion([], error.localizedDescription)
            } else {
                let mealplans = querySnapshot?.documents.compactMap { (queryDocuments) -> Mealplan in Mealplan(dictionary: queryDocuments.data(), mealplanId: queryDocuments.documentID, opened: false, menuItems: [MenuItems(menuItemName: "", menuItemQuantity: "")])!}
                completion(mealplans, nil)
            }
        }
    }

问题出在我的表格视图中，我只看到其中一个膳食计划重复了 planArray.count 次。我认为主要问题是我在哪里重新加载 tableview？

Answer 1

你可以使用 dispatchGroup 来解决这个问题

MealplanCalls.getRestaurants(userId: userId) { (restaurantList, error) in
            if let error = error {
                self.showError(show: "Error", display: error)
            } else {
                var currentPlansArray = [Mealplan]()
                var restaurantIndex = 0
                let group = DispatchGroup()
                
                while (restaurantIndex < restaurantList.count) {
                    group.enter()
                    MealplanCalls.getPlans(restaurantId: restaurantList[restaurantIndex]) { (mealplans, error) in
                        guard let mealplans = mealplans, mealplans.count > 0 else { return }
                        self.planArray.append(contentsOf: mealplans)
                        print("empty : \(self.planArray.count), \(self.planArray)")
                        if let error = error {
                            self.showError(show: "Error", display: error)
                        }

                    group.leave()
                    currentPlansArray.removeAll()
                    restaurantIndex += 1
               }
            }
                
                
                group.notify(queue: DispatchQueue.main, execute: {

                  self.planTable.reloadData()
                })
              
        }
}