Programming Tutorials

  You’ve migrated from Core Data to SwiftData, enticed by the promise of pure Swift syntax and macro magic. The preview works perfectly. But the moment you introduce a background   Task   to fetch API data or perform a batch update, your app terminates with a cryptic   EXC_BAD_ACCESS   or a "context invalid" error. This is the most common hurdle in modern iOS development:  SwiftData concurrency violations. While SwiftData abstracts away the  NSManagedObjectContext  boilerplate, it does not remove the underlying threading rules of the persistence engine. This guide dissects why these crashes occur, explains the strict thread confinement rules, and provides a robust  ModelActor  pattern to fix them permanently. The Root Cause: Thread Confinement & The Abstraction Leak To debug this, you must understand what SwiftData is hiding. Under the hood, SwiftData is still powered by Core Data. A  ModelContext  wraps an  NSManagedO...