Core Data Diagnostics & Migration

Overview

Core Data issues manifest as production crashes from schema mismatches, mysterious concurrency errors, performance degradation under load, and data corruption from unsafe migrations. Core principle 85% of Core Data problems stem from misunderstanding thread-confinement, schema migration requirements, and relationship query patterns—not Core Data defects.

Red Flags — Suspect Core Data Issue

If you see ANY of these, suspect a Core Data misunderstanding, not framework breakage:

• Crash on production launch: "Unresolvable fault" after schema change
• Thread-confinement error: "Accessing NSManagedObject on a different thread"
• App suddenly slow after adding a User→Posts relationship
• SwiftData app needs complex features; considering mixing Core Data alongside
• Schema migration works in simulator but crashes on production
• ❌ FORBIDDEN "Core Data is broken, we need a different database"
  • Core Data handles trillions of records in production apps
  • Schema mismatches and thread errors are always developer code, not framework
  • Do not rationalize away the issue—diagnose it