CoreData Migration new attribute Swift

Question

I have a CoreData database in Swift. I added a new version in which i added 3 more attributes. The problem is that if a user has already added some values to the database, before I added the new attributes to the database, the app will crash. This is due I want to read out the whole database with all its values. But if the user has added some values before I added the new version, then there will be no values in the new added attributes. So I read out the attributes which hold no values. Can I change it so like all old attributes will automatically be something like an empty string, so it won't crash? Or can I catch the error or something?

Answer 1

One way is to write a reader function that throws and in the error handling call a different function which is for the old inputs . PS, would be easier to help you if you post the code

//error type
enum Error: ErrorType{
    case OldInput
}
func fetchFromDatabase() throws {
   //do you fetching 
   if //condition if the new attribute exists {
        //fetch
        return
   }
   throw Error.OldInput
}

//calling it
do {
   try fetchFromDatabase()
} catch (error) {
   fetchFromDatabaseOld()
}