Integrate Combine Into an App

Aug 5 2021 · Swift 5.4, macOS 11.3, Xcode 12.5

Part 2: Integrate with Core Data & Unit Test

08. Use @FetchRequest to Get Core Data Entries

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Previous episode: 07. Create the Core Data Stack Next episode: 09. Test with Given-When-Then

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At this point, we’ve written helper methods to save to and delete from the Core Data database. But once we have the data there, we need a way to fetch it from the database and keep the UI up to date.

// On slide: the signature for @FetchRequest

//On slide:
init(entity: NSEntityDescription, sortDescriptors: [NSSortDescriptor], predicate: NSPredicate?, animation: Animation?)

//On slide:
init(sortDescriptors: [NSSortDescriptor], predicate: NSPredicate?, animation: Animation?)

//On slide:
init(fetchRequest: NSFetchRequest<Result>, animation: Animation?)

//On slide:
init(fetchRequest: NSFetchRequest<Result>, transaction: Transaction)

@Environment(\.managedObjectContext) private var viewContext

if decisionState == .liked {
  JokeManagedObject.save(joke: viewModel.joke,
                         inViewContext: viewContext)
}

.sheet(isPresented: $presentSavedJokes) {
        SavedJokesView()
          .environment(\.managedObjectContext, self.viewContext)
      }

@Environment(\.managedObjectContext) private var viewContext

@FetchRequest(
  sortDescriptors: [NSSortDescriptor(
                        keyPath: \JokeManagedObject.value,
                        ascending: true
                   )],
  animation: .default
) private var jokes: FetchedResults<JokeManagedObject>

ForEach(jokes, id: \.self) { joke in

  Text(self.showTranslation ? joke.translatedValue ?? "N/A"
                            : joke.value ?? "N/A")
    .lineLimit(nil)
}
.onDelete { indices in
  // 2
  self.jokes.delete(at: indices,
                    inViewContext: self.viewContext)
}