SKILL.md
GRDB
Direct SQLite access using GRDB.swift - type-safe Swift wrapper with full SQLite power when you need it.
Quick Reference
| Reference | Load When |
|---|---|
| [Getting Started](references/getting-started.md) | Setting up DatabaseQueue or DatabasePool |
| [Queries](references/queries.md) | Writing raw SQL, Record types, type-safe queries |
| [Value Observation](references/value-observation.md) | Reactive queries, SwiftUI integration |
| [Migrations](references/migrations.md) | DatabaseMigrator, schema evolution |
| [Performance](references/performance.md) | EXPLAIN QUERY PLAN, indexing, profiling |
When to Use GRDB vs SQLiteData
| Scenario | Use |
|---|---|
| Type-safe @Table models | SQLiteData |
| CloudKit sync needed | SQLiteData |
| Complex joins (4+ tables) | GRDB |
| Window functions (ROW_NUMBER, RANK) | GRDB |
| Performance-critical raw SQL | GRDB |
| Reactive queries (ValueObservation) | GRDB |
Core Workflow
- Choose DatabaseQueue (single connection) or DatabasePool (concurrent reads)
- Define migrations with DatabaseMigrator
- Create Record types (Codable, FetchableRecord, PersistableRecord)
- Write queries with raw SQL or QueryInterface
- Use ValueObservation for reactive updates
Requirements
- iOS 13+, macOS 10.15+
- Swift 5.7+
- GRDB.swift 6.0+
Common Mistakes
- Performance assumptions without EXPLAIN PLAN — Assuming your query is fast or slow without checking
EXPLAIN QUERY PLANis guessing. Always profile queries with EXPLAIN before optimizing.
- Missing indexes on WHERE clauses — Queries filtering on non-indexed columns scan the entire table. Index any column used in WHERE, JOIN, or ORDER BY clauses for large tables.
- Improper migration ordering — Running migrations out of order or skipping intermediate versions breaks schema consistency. Always apply migrations sequentially; never jump versions.
- Record conformance shortcuts — Not conforming Record types to
PersistableRecordorFetchableRecordcorrectly leads to silent data loss or deserialization failures. Always implement all required protocols correctly.
- ValueObservation without proper cleanup — Forgetting to cancel ValueObservation when views disappear causes memory leaks and stale data subscriptions. Store the cancellable and clean up in deinit.