Firestore query multiple documents with for loop - ios

Question

I am trying to query multiple documents using a for-loop.
My database set up looks like this:
users -> wishlists -> all the users Wishlists(containing different Wishlists with name) -> wünsche
The items are getting retrieved but in the wrong order. I tried couple of different things but nothing worked so far.
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
}
}
}
}
I am calling this function inside another function that retrieves all the wishlist in the right order:
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()
}
}
*DataSourceArray in the right order: * Main Wishlist, Goals, boost
Output from 2nd print-test: boost, Goals, Main Wishlist

Answer 1

Seems as though you are trying to make a bunch of API calls at once and it is returning values at different times. You could attempt to make your calls synchronously to maintain order or you could try to use dispatch groups like the pseudo code below:
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 }
}