Storing asynchronous Cloud Firestore query results in Swift

Question

I am working on a simple project using Swift 5, SwiftUI and Firebase which cycles through given ids in an array, searching in the Cloud Firestore database for each id, and a

Answer 1

You need a dispatch group in addition to a completion

func convertToNames(arr: [String],completion:@escaping(([String]) -> ())) {

    var newArr : [String] = []
    let g = DispatchGroup()
      for id in arr {
         let docRef = db.collection("users").document(id) 
                 g.enter()
                 docRef.getDocument { (document, error) in
                     if let document = document, document.exists {
                         let dataDescription = document.data().map(String.init(describing:)) ?? "nil"
                         let data = document.get("firstname") ?? "nil"

                         print("gotten data: \(data)")
                         newArr.append(String(describing: data))
                         g.leave()
                     } else {
                         print("Document does not exist")
                         g.leave()
                     }
            }
        }

       g.notify(queue:.main) { 
         print("NEW ARRAY: \(newArr)")
         completion(newArr)
       }
}

Call

convertToNames(arr:<#arr#>) { res in
     print(res)
}