Inter-App Data Migration (migrating data to new app version) - swift

Question

I currently have a Swift iOS app on Apple's App Store. I have many users and I would like to make a new version and help current users migrate to the new version. FYI: the new version is an Ionic app.
Data-wise, my app is using Core Data without any iCloud or sync support. It contains JSON data and also multiple images. So I'd need to bundle the current data and find a way of bringing it to the new ionic app version.
Basically my question is: Is there a way of writing in the app's documents directory and let the new version grab that file to import its data? Is there a way of letting both apps transmit data other than AirDrop or Custom URLs?
I don't want to upload the data remotely, I'd like to do this all locally on the device and also seamlessly so the user don't have to manually do anything.
Suggestions are welcome, thanks!

Answer 1

I would suggest using App Groups to get a shared container. I’m not familiar with Ionic, but this is quite straightforward in native Swift. It allows multiple apps or extensions to access a shared container of data, like the image below:
(Image from https://agostini.tech/2017/08/13/sharing-data-between-applications-and-extensions-using-app-groups/ )
This would require an update to the existing app to copy data to the shared container and then users would have to install the new app while the old one was still installed, because the shared container will be deleted when there are no installed apps using it.
It can be set up like this:
1: Enable App Groups in your project's Capabilities tab (for both apps).
2: Add a new app group and name it something like "group.appDomain.appName" or similar.
3: Now that the App Group is set up, it’s shared container can be used in several ways (User Defaults, NSCoding or Core Data).
For shared User Defaults:
let defaults = UserDefaults.init(suiteName: "group.appDomain.appName")
defaults.set("Example", forKey: "exampleKey")   
defaults.synchronize()
More info from Apple here.
For NSCoding:
let sharedContainerDirectory: URL = FileManager().containerURL(forSecurityApplicationGroupIdentifier: "group.appDomain.appName")!
let sharedArchiveURL: URL = sharedContainerDirectory.appendingPathComponent("whateverYouNeed")
NSKeyedArchiver.archiveRootObject(yourObject, toFile: sharedArchiveURL.path)
For Core Data:
You can set up the container as below. I have taken this code from this answer as I have not actually tried this with Core Data myself.
You use containerURL(forSecurityApplicationGroupIdentifier: "group.appDomain.appName")! to make this work in shared container.
lazy var persistentContainer: NSPersistentContainer = {
/*
The persistent container for the application.
This implementation creates and returns a container, having loaded the store for the application to it.
This property is optional since there are legitimate error conditions that could cause the creation of the store to fail.
*/
let container = NSPersistentContainer(name: "xx")
let appName: String = "xx"
var persistentStoreDescriptions: NSPersistentStoreDescription
let storeUrl = FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: "group.appDomain.appName")!.appendingPathComponent("xx.sqlite")
let description = NSPersistentStoreDescription()
description.shouldInferMappingModelAutomatically = true
description.shouldMigrateStoreAutomatically = true
description.url = storeUrl
container.persistentStoreDescriptions = [NSPersistentStoreDescription(url: FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: "group.com.xxx.xx.container")!.appendingPathComponent("xx.sqlite"))]
container.loadPersistentStores(completionHandler: { (storeDescription, error) in
if let error = error as NSError? {
fatalError("Unresolved error \(error), \(error.userInfo)")
}
})
return container
}()
This answer provides a way to migrate the persistent store.
As I mentioned, I am not familiar with Ionic, so I’m not sure how working in that context might change this technique.
I hope this is helpful.

Answer 2

I would have just left a comment but I am unable to do so.
I was able to see that after loading a native iOS application then a Ionic project with the same bundle structure that the data within Library/Application Support/DisplayName.sqlite was still there and the data within the database still intact. (Note: this is deploying using Xcode not through the App Store)
You can see this using Xcode -> Window -> Devices and Simulators -> Devices tab -> Click on your app -> settings cog -> Download container -> after saving Show package contents
I was unable to use the Ionic SQLite native plugin to open the database for some reason. That is as far as I could get. I think it might have something to do with the space of the Application Support folder.

Answer 3

You can do the transition without using AirDrop or Custom Url. The idea is based on how ionic works. Much of the ionic functionality depends upon the plugins developed by community like working with hardware features.
Dealing with device specific features are done in native codes then JS wrapper classes are created for making a bridge between your code and native code.
I would suggest you to write native code which will access the data and files from CoreData and then use the cordova plugin tech to setup communication between the native code and the ionic code. here is a good post on Creating Custom Plugin for ionic and a sample github project