#indiedev #irishmusic #iosdev #buildInPublic

The app started as objective-C using an in-memory data model persisted to Apple plists. I added #coredata classes soon after. Currently the data model has 4 major domain classes mirrored by core data classes, and some additional classes for convenience.

I've converted the majority of the code to Swift. I've kept all rendering and editing logic (display, audio, export etc) in Swift, using core data only for persistence and search. 2/n

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To zoom in a bit on the problem at hand: #cloudKit is the obvious choice for sync between devices. Apple's documentation would have you believe that all you need to do is change your NSPersistentContainer to a NSPersistentCloudKitContainer and all will be well!
Not so fast.
First of all, the coredata and cloudkit data models have to be compatible. In this case, we find the dreaded OrderedRelationship in two places.
3/n

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Tune to TuneSet is a many:many relationship ordered by the tunes’ play order. Functionally, the user can add Tunes to TuneSets and re-order or remove them. We must convert the many:many relationship to an intermediate object with an ordering attribute that we can use when we retrieve a TuneSet. We will have to be able to manipulate the ordering attribute to let the user drag Tunes to re-order them in the UI.
4/n

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The second case is a little more complex. Collections can contain Tunes and TuneSets. By default, they are time-ordered when users add to their contents. Users can also reorder them, and I've had requests (not yet implemented) for alphabetical and most-recent first ordering.
A superclass (Searchable) inherited by both TuneSet and Tune allows for containment of both in a Collection.

5/n

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diagrams of where we are so far…
6/n

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Now we've sketched out a workable data model that works in both coreData and CloudKit, we need to work out:
- how to migrate from the existing model to the new one without losing data.
- how to handle merging databases from different devices given that the user might have duplicate entries or collections with different members or different ordering

7/n

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Apple has improved their migration support since I last looked - migrating to the data model outlined above would work as a staged migration:
- add the new entities and any attributes needed to define ordering or deduplication
- populate the intermediate attributed relationships
- delete the old entities

https://developer.apple.com/documentation/coredata/staged-migrations

Now we can safely move from NSPersistentContainer to a NSPersistentCloudKitContainer

8/n

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As an aside - I've learned a lot about CoreData and CloudKit from @fatbobman's blog.

https://fatbobman.com/en/posts/coredatawithcloudkit-1/

9/n

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There is some Apple demo code from WWDC 2022 that gives an example of deduplication on CloudKit sync. It's a simplified demo but it does give an example of a many:many (unordered) relationship. Let's see if we can get it running.
https://developer.apple.com/documentation/coredata/synchronizing-a-local-store-to-the-cloud

10/n

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Got the demo working after some annoying debug sessions. Seems like it has not been revisited since 2022, and iOS 18 changed the behaviour of collectionView.dequeueReusableCell - as of iOS 18 it asserts if you call it outside of cellForItemAt indexpath. it was being called in awakeFromNib to set a font.

You would think that a company with the resources of Apple would at a minimum task interns to COMPILE AND RUN demos called out in the docs 11/n

#iosdev #buildInPublic #coredata #cloudKit I also have make sure I'm selecting the Private database and the com.apple.coredata.cloudkit'recordName' is not marked queryable

https://lyons.app/2021/07/05/how-to-fix-field-recordname-is-not-marked-queryable-in-cloudkit/

gave me the answer: I have to modify the schema by adding a queryable index called recordName to the recordName metadata field for each record type so I can view the records. I also have make sure I'm selecting the Private database and the com.apple.coredata.cloudkit zone.
12/n
Edit: to fix link

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Enough for tonight. Tomorrow I'll start prototyping the migration from explicitly ordered many:many to implicitly ordered via intermediate attributed relationship objects.

13/n

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So the next question is - create a purpose-built prototype to experiment with attributed relationships or bang away at a disposable branch of my main project? I know what I _should_ do... And it will make things easier to share here without distractions. So a new project using Storyboard (i.e. UIKit) template with CoreData. Minimum deployment will be iOS 17. No CloudKit as yet, I want to be able to test migration from ordered many:many .

14/n

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Roughed in a little prototype - UI mostly done, some test classes to create Tunes and TuneSets. Tomorrow rough in Collections. Nice that UIKit now lets us add UISplitViewControllers as tabs on UITabControllers.

15/n

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Some random observations while developing the prototype/testbed app:
Why doesn't Apple put the superclass in the Swift version of the docs for #UIKit ? It's still there in the Obj-C version. There's lot's of times when I need to see the APIs for the superclass.
I'm using #UIKit, not SwiftUI. I've done a bit of playing with SwiftUI, but I've been using UIKit since 2009, and I like it better for CoreData related stuff, so I will stick with it.

16/n

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Over the years I've been using Storyboards less and less. I now tend to build VCs programmatically using UIStackViews.

The shipping version manages a single 3-pane UISplitViewController and transitions manually to a tab bar when necessary. This works back to iOS 15, but it's annoying to debug and makes assumptions about the frameworks that may not be true going forward.

17/n

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I’m using a UITabBarController with UISplitViewControllers as the individual tabs for the prototype. This works nicely in iOS 26, but not in iOS 18, and no hope of getting it to run on anything earlier.

18/n

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I know that UITableViewControllers are sort-of soft-deprecated, but they're a lot easier to use for this sort of prototyping than UICollectionViewControllers. Also, diffable data sources are recommended but are way overkill for most situations and hard to understand.

19/N

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Most of this went together pretty easily but I spent way too much time trying to figure out how to get my tableHeaderView to properly respect changing margins as sidebars and splitviewcontrollers resize and show/hide.

20/n

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I couldn't figure out how to do it programmatically, but I had to make it a subclass of UITableViewHeaderFooterView, add it as a subview of the TableView in the storyboard and then put my stackView as a subview of the contentView, with explicit constraints, which magically obeys the changing margins.

21/n

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You can find what I've done so far at:

https://github.com/Wil-Macaulay/attributedRelationships

22/n

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Going to need some unit tests. Looks like the new Swift Testing framework is pretty neat, so let's try using that. I’m not a TDD guy, so this may be a rabbit hole that might take a while, but probably worth a try. Start by adding a test target as per the WWDC 2024 video https://developer.apple.com/videos/play/wwdc2024/10179

23/n

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Add a new test target from the file menu…
Odd that it doesn't follow the same deployment info as the main target (ios 18) , but defaults to iOS 26.1 (the version of Xcode I’m running)

24/n