How to add parameters to existing model when objects already saved? - ios

Question

I have a Bill class which contains a few instances of bills that are saved in a plist file to the documents directory using NSKeyedArchiver.
class Bill: NSObject, NSCoding {
required init?(coder aDecoder: NSCoder) {
name = aDecoder.decodeObject(forKey: "Name") as! String
moPayment = aDecoder.decodeDouble(forKey: "Payment")
super.init()
}
override init() {
super.init()
}
var name = "Bill Name"
var moPayment = 0.0
func encode(with aCoder: NSCoder) {
aCoder.encode(name, forKey: "Name")
aCoder.encode(moPayment, forKey: "Payment")
}
}
func saveBillItems(_ bills: [Bill]) {
let data = NSMutableData()
let archiver = NSKeyedArchiver(forWritingWith: data)
archiver.encode(bills, forKey: "BillItems")
archiver.finishEncoding()
data.write(to: dataFilePath(), atomically: true)
}
func loadBillItems() {
let path = dataFilePath()
if let data = try? Data(contentsOf: path) {
let unarchiver = NSKeyedUnarchiver(forReadingWith: data)
bills = unarchiver.decodeObject(forKey: "BillItems") as! [Bill]
unarchiver.finishDecoding()
}
}
All of this works as expected but now I am trying to add an additional parameter to record paidStatus.
class Bill: NSObject, NSCoding {
required init?(coder aDecoder: NSCoder) {
...
status = aDecoder.decodeObject(forKey: "Status") as! PaidStatus
super.init()
}
...
var status = PaidStatus.unpaid
enum PaidStatus {
case overdue
case upcoming
case unpaid
case paid
}
...
func encode(with aCoder: NSCoder) {
...
aCoder.encode(status, forKey: "Status")
}
}
func saveBillItems(_ bills: [Bill]) {
...
}
func loadBillItems() {
...
}
When I try to run the app now, I get an error: "Unexpectedly found nil..."
status = aDecoder.decodeObject(forKey: "Status") as! PaidStatus
due to trying to load existing bill objects that don't have this parameter.
Is there a way to add this parameter to my existing objects without having to delete them and recreate them again from scratch?

Answer 1

Since your object may not have a value, you need to use an optional downcast, not a forced downcast. Since status is not an optional, you can use a nil coalescing operator to provide a default value
status = aDecoder.decodeObject(forKey: "Status") as? PaidStatus ?? .unpaid