How can I get Document Data and Reference Data at same time ?(Firestore, Swift) - swift

Question

I'm trying to get Document Data and Reference Data at the same time, and put data in to custom struct which consist with String Array.
When I run code below, only DocumentReference type "item1_" and "item2_" are appended.
Collection "section" has several documents. Each document has 2 Document references.
I can get right DocumentReference but I can't read it's data in same function.
How can I get both Data from Firestore?
func getall_sec(top: String, mid: String){ref.collection("top_hierarchy").document(top).collection("mid_hierarchy").document(mid).collection("section").addSnapshotListener(){ (snap, err) in
guard let docs = snap else {
self.nosecs = true
return
}
if docs.documentChanges.isEmpty{
self.nosecs = true
return
}
docs.documentChanges.forEach { (doc) in
if doc.type == .added{
let item1_ = doc.document.data()["item1"] as! DocumentReference
let item2_ = doc.document.data()["item2"] as! DocumentReference
item2_.getDocument(){ (querySnapshot, err) in
if let err = err {
print("Error getting documents: \(err)")
} else {
self.item2_name = querySnapshot?.data()?["low"] as! String
self.item2_ImageName = querySnapshot?.data()?["ImageName"] as! String
}
}
item1_.getDocument(){ (querySnapshot, err) in
if let err = err {
print("Error getting documents: \(err)")
} else {
self.item1_name = querySnapshot?.data()?["low"] as! String
self.item1_ImageName = querySnapshot?.data()?["ImageName"] as! String
}
}
self.sections.append(SectionModel(id: doc.document.documentID, item_name1: self.item1_name, item_ImageName1: self.item1_ImageName, item_name2: self.item2_name, item_ImageName2: self.item2_ImageName))
}
}
}
}

Answer 1

The main issue is that getDocument is asynchronous and the the self.sections.append code will actually execute before the code in the closures following the two get functions.
item2_.getDocument(){ (querySnapshot2, err2) in
//this code will execute at some point
}
item1_.getDocument(){ (querySnapshot1, err1) in
//this code will execute at some point
}
//this code will execute before the code in the two above getDocument closures.
self.sections.append(SectionModel(id: doc.document.documentID...
one solution is to nest the calls so they execute in order (this is not the best solution but demonstrates the concept)
item2_.getDocument(){ (querySnapshot, err) in
item1_.getDocument(){ (querySnapshot, err) in
self.sections.append(SectionModel(id: doc.document.documentID...
}
}