使用for循环恢复查询多个文档

Question

我正在尝试使用for-loop查询多个文档。

我的数据库设置如下所示：

用户 -> 愿望清单 ->所有用户 愿望清单(包含带有name的不同愿望清单( -> 温舍

正在检索项目，但顺序错误。我尝试了几件不同的事情，但到目前为止没有任何效果。

func getWishes() {
let db = Firestore.firestore()
let userID = Auth.auth().currentUser!.uid
var counter = 0
for list in self.dataSourceArray {
print(list.name) // -> right order
}
for list in self.dataSourceArray {
db.collection("users").document(userID).collection("wishlists").document(list.name).collection("wünsche").getDocuments() { ( querySnapshot, error) in
print(list.name) // -> wrong order
if let error = error {
print(error.localizedDescription)
}else{
// create new Wish array
var wList: [Wish] = [Wish]()
for document in querySnapshot!.documents {
let documentData = document.data()
let wishName = documentData["name"]
wList.append(Wish(withWishName: wishName as! String, checked: false))
}
self.dataSourceArray[counter].wishData = wList
counter += 1
}
}
}
}

我在另一个函数中调用此函数，该函数以正确的顺序检索所有wishlist：

func getWishlists() {
let db = Firestore.firestore()
let userID = Auth.auth().currentUser!.uid
db.collection("users").document(userID).collection("wishlists").order(by: "listIDX").getDocuments() { ( querySnapshot, error) in
if let error = error {
print(error.localizedDescription)
}else {
// get all documents from "wishlists"-collection and save attributes
for document in querySnapshot!.documents {
let documentData = document.data()
let listName = documentData["name"]
let listImageIDX = documentData["imageIDX"]
// if-case for Main Wishlist
if listImageIDX as? Int == nil {
self.dataSourceArray.append(Wishlist(name: listName as! String, image: UIImage(named: "iconRoundedImage")!, wishData: [Wish]()))
// set the drop down menu's options
self.dropDownButton.dropView.dropDownOptions.append(listName as! String)
self.dropDownButton.dropView.dropDownListImages.append(UIImage(named: "iconRoundedImage")!)
}else {
self.dataSourceArray.append(Wishlist(name: listName as! String, image: self.images[listImageIDX as! Int], wishData: [Wish]()))
self.dropDownButton.dropView.dropDownOptions.append(listName as! String)
self.dropDownButton.dropView.dropDownListImages.append(self.images[listImageIDX as! Int])
}
// reload collectionView and tableView
self.theCollectionView.reloadData()
self.dropDownButton.dropView.tableView.reloadData()
}
}
self.theCollectionView.isHidden = false
self.getWishes()
}
}

*数据源数组按正确的顺序排列： *主要愿望清单，目标，提升

第 2print测试的输出：提升、目标、主要愿望清单

Answer 1

似乎您正在尝试一次进行一堆 API 调用，并且它在不同的时间返回值。您可以尝试同步进行调用以维持秩序，也可以尝试使用调度组，如下面的伪代码：

let myGroup = DispatchGroup()
struct DataItem {
let order: Int
let data: DataYouWantToSave
}
var fetchedData = [DataItem]()
for i in list {
myGroup.enter()
let dataItem = DataItem()
dataItem.order = i
db.collection...
print("Finished request (i)")
dataItem.data = DataYouWantToSave
fetchedData.apped(dataItem)
myGroup.leave()
}
}
myGroup.notify(queue: .main) {
print("Finished all requests.")
// Reorder your array of data items here.
let sortedArray = fetchedData.sorted(by: { $0.order > $1.order })
// If you just want the array of data values
let newData: [DataYouWantToSave] = sortedArray.map { $0.data }
}