Is there any way to implement a taskGroup to run in parrarel inside another taskGroup? - swift

Question

I am using Firebase to fetch some data from it with a Continuation. Before resuming the continuation I want to run a group of async tasks inside(fetch other data). This would let me achieve maximum concurrency.
I have tried two methods to do this, both does not work.
This is what I have tried first trying to use inside a continuation a taskGroup.(Code Below). The error is in comment.
First Option
try? await withThrowingTaskGroup(of: Void.self) { group in
for referencePosts in referencePostsDict.keys {
group.addTask {
return try! await self.fetchPost(reference: referencePosts)
}
}
func fetchPost(reference: String) async throws -> Void{
var db_ref = Database.database(url:FIREBASEURL.url)
.reference()
.child("posts")
.child(reference)
typealias postContinuation = CheckedContinuation<Void,Error>
return try await withCheckedThrowingContinuation{
(continuation : postContinuation) in
db_ref.observeSingleEvent(of: .value) { data in
if data.exists(){
var three = data.value as! [String : Any]
withThrowingTaskGroup(of: Void.self) { group in //async' call in a function that does not support concurrency
(three["picturePaths"] as! [String : String]).forEach { key, value in
if key != "O"{
group.addTask {
try? await self.fetchPictureDataL(picRef: key)
}
self.threePictures[key] = value
}
}
}
self.threePosts[reference] = three
continuation.resume(returning: ())
}else{
continuation.resume(returning: ())
}
}
}
}
func fetchPictureDataL(picRef : String) async throws ->Void{
var db =Database
.database(url:FIREBASEURL.url)
.reference()
.child("pictures").child(picRef)
typealias postContinuation = CheckedContinuation<Void,Error>
return try await withCheckedThrowingContinuation{
(continuation : postContinuation) in
db.observeSingleEvent(of: .value) { data in
self.threePicturesFetched[picRef] = three as! [String : Any]
continuation.resume(returning: ())
}
}
}
I commented the code where the compiler reports a problem.
Second Option
fetchCheckIn2 method is modified to return a [String]
This is the second method where I have tried to achieve the same result different, to mention the fetchCheckIn2 method is modified to return a [String].
What I want to achieve is that the fetchPictureDataL will run in parallel inside a Task or group, and will not run awaiting each other to finish.
//fetching all references
try! await withThrowingTaskGroup(of: [String].self) { firstGroup in
for referenceCheckIn in reference_checkInInt_dictionary.keys {
firstGroup.addTask {
return try await self.fetchCheckIn2(reference: referenceCheckIn)
}
}
for try await pictureArray in firstGroup {
if pictureArray.count != 0 {
for pic in pictureArray {
try! await self.fetchPictureDataL(picRef: pic)
}
}
}
}
Trying to achieve
I want to achieve parallelism even with fetchPictureDataL method?
If not clear why I am trying to do this, please read the use of case.
Use of this case:
I have social media app with posts. I have a list of paths in order to fetch the post. Each post contains an array of other paths which are pictures.
I want to fetch posts parrarel and also fetch the pictures in parrarel, in a taskGruop, so all this fetch of post+picture is awaited and can be displayed to User.
Thank you