Get Firebase document objects as Swift object - ios

Question

I try to implement a simple shopping list swift application for iOS as a personal project. I did follow a guide for iOS on youtube.
My question is how do I parse the Item object from firebase to my ShoppingListItem swift object? If I execute the following code, it doesn't show any error message but it does not show any results either. If I uncomment all "items" lines, it shows the expected results without the item information.
Here is a screenshot from the firebase console of my firebase firestore structure / example object
Thanks in advance!
ShoppingListItem.swift
import Foundation
import FirebaseFirestore
protocol DocumentSerializable {
init?(dictionary: [String: Any])
}
struct ShoppingListItem {
var shoppingItemID: String
var priority: Int
var quantity: Int
var item: Item
var dictionary: [String: Any] {
return [
"shoppingItemID": shoppingItemID,
"priority": priority,
"quantity": quantity,
"item": item,
]
}
}
extension ShoppingListItem: DocumentSerializable {
init?(dictionary: [String : Any]) {
guard let shoppingItemID = dictionary["shoppingItemID"] as? String,
let priority = dictionary["priority"] as? Int,
let quantity = dictionary["quantity"] as? Int,
let item = dictionary["item"] as? Item
else { return nil }
self.init(shoppingItemID: shoppingItemID, priority: priority, quantity: quantity, item: item)
}
}
struct Item {
var itemID: String
var lastPurchase: String
var name: String
var note: String
var picturePath: String
var dictionary: [String: Any] {
return [
"itemID": itemID,
"lastPurchase": lastPurchase,
"name": name,
"note": note,
"picturePath": picturePath,
]
}
}
extension Item: DocumentSerializable {
init?(dictionary: [String : Any]) {
guard let itemID = dictionary["itemID"] as? String,
let lastPurchase = dictionary["lastPurchase"] as? String,
let name = dictionary["name"] as? String,
let note = dictionary["note"] as? String,
let picturePath = dictionary["picturePath"] as? String else { return nil }
self.init(itemID: itemID, lastPurchase: lastPurchase, name: name, note: note, picturePath: picturePath)
}
}
Get Data call in TableViewController.swift
db.collection("shoppingList").getDocuments(){
querySnapshot, error in
if let error = error {
print("error loading documents \(error.localizedDescription)")
} else{
self.shoppingArray = querySnapshot!.documents.flatMap({ShoppingListItem(dictionary: $0.data())})
DispatchQueue.main.async {
self.tableView.reloadData()
}
}
}

Answer 1

I used the Codable protocol.
I used this as an extension to the Encodable Protocol:
extension Encodable {
/// Returns a JSON dictionary, with choice of minimal information
func getDictionary() -> [String: Any]? {
let encoder = JSONEncoder()
guard let data = try? encoder.encode(self) else { return nil }
return (try? JSONSerialization.jsonObject(with: data, options: .allowFragments)).flatMap { $0 as? [String: Any]
}
}
}
Then I use this to decode:
extension Decodable {
/// Initialize from JSON Dictionary. Return nil on failure
init?(dictionary value: [String:Any]){
guard JSONSerialization.isValidJSONObject(value) else { return nil }
guard let jsonData = try? JSONSerialization.data(withJSONObject: value, options: []) else { return nil }
guard let newValue = try? JSONDecoder().decode(Self.self, from: jsonData) else { return nil }
self = newValue
}
}
Make your two structs conform to Codable (Item first, then ShoppingListItem). Of course, this may not work for the existing data stored in Firestore. I would first put data into Firestore via the getDictionary() (in a new collection), then try to read it back into your tableView.

Answer 2

You may also want to print the actual error when trying to Decode your data, this will greatly help you pinpoint the data error if there's any.
extension Decodable {
/// Initialize from JSON Dictionary. Return nil on failure
init?(dictionary value: [String:Any]) {
guard JSONSerialization.isValidJSONObject(value) else {
return nil
}
do {
let jsonData = try JSONSerialization.data(withJSONObject: value, options: [])
let newValue = try JSONDecoder().decode(Self.self, from: jsonData)
self = newValue
}
catch {
log.error("failed to serialize data: \(error)")
return nil
}
}
}