Observers

[ryangittings]

It'd be great to be able to observe changes to (similar to token = await items.observe(on: self) { [weak self] _, changes in in realm?

[mbrandonw]

Hi @ryangittings, can you explain a bit more how you plan to use this tool?

There are a few ways to do this with the library. First, the property wrappers like @FetchAll work seamlessly in SwiftUI views already, and observation is handled automatically:

struct FeatureView: View {
  @FetchAll var reminders: [Reminder]
  var body: some View {
    // Changes to 'reminders' will be observed by the view
    ForEach(reminders) { … }
  }
}

This works with @Observable models too:

@Observable class FeatureModel {
  @ObservableIgnored  // This is needed due to a quirk of @Observable, but observation still works
  @FetchAll var reminders: [Reminder]
}
struct FeatureView: View {
  let model: FeatureModel
  var body: some View {
    // Changes to 'model.reminders' will be observed by the view
    ForEach(model.reminders) { … }
  }
}

Further, each property wrapper has a projected value that can give you a publisher:

class FeatureViewController: UIViewController {
  @FetchAll var reminders: [Reminder]
  func viewDidLoad() {
    $reminders.publisher
      .sink { … }
      .store(in: &cancellables)
  }
}

And if you want to depend on our Swift Navigation library, then there is a general purpose observe { … } tool that can be used:

class FeatureViewController: UIViewController {
  @FetchAll var reminders: [Reminder]
  func viewDidLoad() {
    observe { [weak self] in 
      guard let self else { return }

      // The act of accessing 'reminders' causes its changes to be observed.
      reloadDataSource(reminders)
    }
  }
}

We have a case study for this latter style that shows how to power a UICollectionView from SQLiteData:

sqlite-data/Examples/CaseStudies/UIKitDemo.swift

Lines 76 to 82 in 0eed823

	observe { [weak self] in
	guard let self else { return }
	var snapshot = NSDiffableDataSourceSnapshot<Section, Fact>()
	snapshot.appendSections([.facts])
	snapshot.appendItems(facts, toSection: .facts)
	dataSource.apply(snapshot, animatingDifferences: true)
	}

[ryangittings]

Thanks for the reply!

I currently don't use it for visual reasons - it's for syncing local state to remote basically. I don't think any of the examples above are ideal? It's so easy with Realm , e.g.:

switch changes {
        case .update(let results, _, let insertions, let modifications):
            for insertionIndex in insertions {
            }

            for modificationIndex in modifications {
            }
        case .error(let error):
        }

[mbrandonw]

From your code snippet it seems that you are asking for the deltas in changes to your database? If so, SQLiteData doesn't provide a direct tool for this because it's not really necessary. You have all the power of SQLite at your fingertips, and database triggers are the best tool for this. You can install an insert/update/delete trigger on your table and be immediately notified of each modification.

This is how we implemented the SyncEngine in the library. We install triggers on the user's table to be notified of each insert/update/delete, and then we enqueue saveRecord and deleteRecord changes to the sync engine to be processed later.