Handling documentID in FirebaseFirestoreSwift is really confusing - swift

Question

I have to query a slew of collections and the models are always defined something like this:
struct Order : Identifiable, Codable {
#DocumentID var id : String?
let fieldOne : String?
let fieldTwo : Int?
enum CodingKeys : String, CodingKey {
case id // (had to comment this out)
case fieldOne
case fieldTwo
}
}
Today, I spent all day trying to figure out why I couldn't load documents from for one particular collection. I was getting a snapshot with documents but could not convert and populate them into an array. After hours of trial and error I commented out the "case id" in the enum and got it to work.
Any idea why this is happening?
Here's a query which works WITH the case id:
listener = db.collection("Meal_Plans").whereField("userId", isEqualTo: userEmail).order(by: "timeOfCreation", descending: true).addSnapshotListener({ (querySnapshot, error) in
if let error = error {
print("error in mp query: \(error.localizedDescription)")
} else {
guard let documents = querySnapshot?.documents else {
print("No mealplans")
return
}
let mealplanArray: [Mealplan] = documents.compactMap { queryDocumentSnapshot -> Mealplan? in
return try? queryDocumentSnapshot.data(as: Mealplan.self)
}
let planViewModel = mealplanArray.map({return PlanViewModel(mealplan: $0)})
DispatchQueue.main.async {
if mealplanArray.count > 0 {
self.planViewModelDelegate?.plansFetched(self.updateHour(sourcePlans: planViewModel))
}
}
}
})
And this is the one WITHTOUT:
listener = db.collection("Placed_Orders").whereField("userId", isEqualTo: userId).whereField("status", isLessThan: 410).order(by: "status", descending: false).order(by: "nextOrderDate", descending: false).addSnapshotListener({ (documentSnapshot, error) in
if let error = error {
print("error")
self.orderCallback?(error.localizedDescription, nil, .error)
} else {
print("empty")
guard let documents = documentSnapshot?.documents else {
return }
if documents.isEmpty {
self.orderCallback?("No orders found", nil, .error)
return
} else {
print("snapshot count: \(documents.count)")
let orderArray: [Order] = documents.compactMap { queryDocumentSnapshot -> Order? in
return try? queryDocumentSnapshot.data(as: Order.self)
}
let orderViewModel = orderArray.map({ return OrderViewModel(order: $0)})
print("array count: \(orderArray.count)")
DispatchQueue.main.async {
print("status: \(orderViewModel)")
self.orderCallback?(nil, orderViewModel, .success)
}
}
}
})
The differences are rather subtle. In both cases I am using a snapshot listener to query the snapshot and populate it into an array and then map that array into a view model.
Yet, in the latter case, I have to comment out the case id for the identifiable field. I need the ID so need to see if it's working but would like to know why I have to comment out the case id.