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3.9 KiB
3.9 KiB
name, description
| name | description |
|---|---|
| realm-migration-ref | Complete migration guide from Realm to SwiftData — pattern equivalents, threading models, schema strategies, CloudKit sync transition |
Realm to SwiftData Migration Reference
URGENT: Realm Device Sync sunsets September 30, 2025. Complete migration guide to prevent data loss.
Overview
Comprehensive reference for migrating from Realm to SwiftData without losing user data or breaking threading patterns. Covers pattern equivalents, schema migration strategies, and CloudKit sync transition.
What's Covered
Pattern Equivalents
Model Definitions
Object→@Model@Persisted→@Attribute/@Relationship- Primary keys and indexing
- Inverse relationships
Queries
results(ofType:)→@Query/FetchDescriptor- Predicates and sorting
- Lazy loading vs eager fetching
- Performance characteristics
Threading Models
- Realm's thread-confined objects → SwiftData's ModelContext
- Background writes → ModelContext on background actors
- Freeze patterns → value snapshots
- Notifications → observation framework
Schema Migration
Data Migration Strategies
- Export Realm data to JSON/SQLite
- Batch import into SwiftData
- Validation and integrity checks
- Rollback strategies
Schema Mapping
- Property type conversions
- Relationship restructuring
- Embedded objects → nested models
- List/Array handling
CloudKit Sync Transition
From Realm Device Sync
- Atlas Device Sync → CloudKit
- Conflict resolution differences
- Authentication changes
- Network Reachability patterns
When to Use This Reference
Use this reference when:
- Planning migration from Realm to SwiftData
- Converting Realm Object models to @Model
- Replacing Realm Device Sync with CloudKit
- Dealing with legacy Realm codebases
- Before September 30, 2025 (Realm Device Sync sunset)
Migration Timeline
1. Audit (Week 1)
- Inventory all Realm models
- Document threading patterns
- List Device Sync dependencies
2. Schema Design (Week 2)
- Design SwiftData @Model equivalents
- Plan relationship mappings
- CloudKit schema design
3. Data Migration (Week 3-4)
- Export Realm data
- Import to SwiftData
- Validate integrity
- Test rollback
4. Code Migration (Week 4-6)
- Replace Realm queries with @Query
- Update threading patterns
- Implement CloudKit sync
- Remove Realm dependencies
5. Testing (Week 7-8)
- User acceptance testing
- Performance validation
- Cloud sync verification
- Production rollout plan
Key Differences
| Realm | SwiftData | Notes |
|---|---|---|
| Thread-confined objects | ModelContext per thread | Must extract values before crossing threads |
realm.write {} |
modelContext.save() |
Explicit vs automatic saving |
| Device Sync | CloudKit | Different conflict resolution |
| Lazy relationships | Eager by default | Performance implications |
| Notifications | @Query observation |
Different update patterns |
Related Skills
- swiftdata – SwiftData implementation patterns
- database-migration – Safe schema evolution
- core-data-diag – Core Data troubleshooting (if considering Core Data instead)
Documentation Scope
This is a reference skill — comprehensive migration guide without mandatory workflows.
Reference includes
- Pattern equivalents catalog
- Threading model comparisons
- Schema migration strategies
- CloudKit sync patterns
- Real-world migration scenarios
Urgency
Realm Device Sync sunsets September 30, 2025
After this date:
- No new Device Sync apps accepted
- Existing apps continue but deprecated
- Migration required for long-term support
Start migration planning now if using Realm Device Sync.
Size
28 KB - Complete migration reference with pattern catalog