Realm Swift Migration to add primary key - Not writing data - swift

Question

I am using RealmSwift and I want to add a new Primary Key to one of my objects.
I have updated the Realm Object to this
class Trip: Object {
dynamic var id = ""
dynamic var start = ""
dynamic var startAddress = ""
dynamic var end = ""
dynamic var endAddress = ""
dynamic var purpose = ""
dynamic var distance = 0.0
dynamic var tripDate = NSDate()
dynamic var month = 0
dynamic var year = 0
dynamic var isWalking = false
dynamic var isReturn = false
func primaryKey() -> String {
return id
}
}
And now I want to migrate to the new version and insert a UUID String as the primary key for any existing record.
The migration works in that the new 'id' field is created, but the UUID strings are not written into the record. No errors displayed on console.
This is what I have added to my AppDelegate application(application:didFinishLaunchingWithOptions:)
I must be missing something, but I cannot determine what, from the documentation or examples on the Realm site.
let config = Realm.Configuration(
// Set the new schema version. This must be greater than the previously used
// version (if you've never set a schema version before, the version is 0).
schemaVersion: 1,
// Set the block which will be called automatically when opening a Realm with
// a schema version lower than the one set above
migrationBlock: { migration, oldSchemaVersion in
// We haven’t migrated anything yet, so oldSchemaVersion == 0
if (oldSchemaVersion < 1) {
// Nothing to do!
// Realm will automatically detect new properties and removed properties
// And will update the schema on disk automatically
}
})
// Tell Realm to use this new configuration object for the default Realm
Realm.Configuration.defaultConfiguration = config
// Now that we've told Realm how to handle the schema change, opening the file
// will automatically perform the migration
let realm = try! Realm()
Realm.Configuration.defaultConfiguration = Realm.Configuration(
schemaVersion: 1,
migrationBlock: { migration, oldSchemaVersion in
if (oldSchemaVersion < 1) {
// The enumerate(_:_:) method iterates
// over every Trip object stored in the Realm file
migration.enumerate(Trip.className()) { oldObject, newObject in
let id = NSUUID().UUIDString
newObject!["id"] = id
}
}
})

Answer 1

The code you've provided sets the default configuration with your migration block after you've already opened the Realm. You need to set the default configuration prior to opening the default Realm in order for the migration block to be used.