SwiftData Migration Diagnostics

Overview

SwiftData migration failures manifest as production crashes, data loss, corrupted relationships, or simulator-only success. Core principle 90% of migration failures stem from missing models in VersionedSchema, relationship inverse issues, or untested migration paths—not SwiftData bugs.

Red Flags — Suspect SwiftData Migration Issue

If you see ANY of these, suspect a migration configuration problem:

• App crashes on launch after schema change
• "Expected only Arrays for Relationships" error
• "The model used to open the store is incompatible with the one used to create the store"
• "Failed to fulfill faulting for [relationship]"
• Migration works in simulator but crashes on real device
• Data exists before migration, gone after
• Relationships broken after migration (nil where they shouldn't be)
• ❌ FORBIDDEN "SwiftData migrations are broken, we should use Core Data"
  • SwiftData handles millions of migrations in production apps