/axiom-data

name: axiom-data
description: Use when working with ANY data persistence, database, storage, CloudKit, migration, or serialization. Covers SwiftData, Core Data, GRDB, SQLite, Realm, CloudKit sync, file storage, Codable, migrations.
license: MIT

Data & Persistence

**You MUST use this skill for ANY data persistence, database, storage, CloudKit, or serialization work.**

<!-- AXIOM_AUDITOR_INLINE_BEGIN — rewritten for Codex by scripts/build-codex.ts; do not hand-edit --> > **Auditors are skills here.** Where this router says "Launch `some-auditor` agent", invoke the > matching Codex skill instead — same procedure, no Claude Code agent required. > > Available: `axiom-audit-codable`, `axiom-audit-core-data`, `axiom-audit-database-schema`, `axiom-audit-grdb-performance`, `axiom-audit-icloud`, `axiom-audit-storage`, `axiom-audit-swiftdata`. > > The ones that shell out — builds, tests, simulators, crash symbolication — need shell access to run. <!-- AXIOM_AUDITOR_INLINE_END -->

When to Use

Use this skill when working with:

• Databases (SwiftData, Core Data, GRDB, SQLiteData)
• Schema migrations
• CloudKit sync
• File storage (iCloud Drive, local storage)
• Data serialization (Codable, JSON)
• Storage strategy decisions
• Keychain / secure credential storage
• Encryption, signing, key management (CryptoKit)

Quick Reference

| Symptom / Task | Reference | |----------------|-----------| | SwiftData @Model, @Query, ModelContext, sectioned queries / ResultsObserver / @Attribute(.codable) / dynamic compound predicates (`OS27`) | See `skills/swiftdata.md` | | SwiftData schema migration, VersionedSchema | See `skills/swiftdata-migration.md` | | SwiftData migration crashes, data loss | See `skills/swiftdata-migration-diag.md` | | Migrating from Realm to SwiftData | See `skills/realm-migration-ref.md` | | SwiftData vs SQLiteData decision | See `skills/sqlitedata-migration.md` | | GRDB queries, upsert, ValueObservation, DatabaseMigrator, encryption | See `skills/grdb.md` | | GRDB performance, indexes, EXPLAIN QUERY PLAN, cursors, observation not firing | See `skills/grdb-performance.md` | | Full-text search (FTS5) in GRDB or SQLiteData | See `skills/sqlite-fts-ref.md` | | Storing or querying JSON inside a SQLite column (JSON1, JSONB) | See `skills/sql-json-ref.md` | | GRDB shared across app + widget/extension (App Group) | See `skills/grdb-app-groups.md` | | SQLiteData @Table, CRUD, SyncEngine | See `skills/sqlitedata.md` | | SQLiteData advanced patterns, CTEs, views | See `skills/sqlitedata-ref.md` | | `@Shared` / `@SharedReader`, appStorage or fileStorage persistence, custom SharedKey, `isLoading` / `loadError` on `@FetchAll` | See `skills/swift-sharing.md` | | Core Data stack, relationships, concurrency | See `skills/core-data.md` | | Core Data migration crashes, thread errors | See `skills/core-data-diag.md` | | ANY schema migration safety | See `skills/database-migration.md` | | Codable, JSON encoding/decoding | See `skills/codable.md` | | Cloud sync architecture, offline-first | See `skills/cloud-sync.md` | | CloudKit, CKSyncEngine, CKRecord | See `skills/cloudkit-ref.md` | | iCloud Drive, ubiquitous containers | See `skills/icloud-drive-ref.md` | | Cloud sync errors, conflict resolution | See `skills/cloud-sync-diag.md` | | Storage strategy, where to store data | See `skills/storage.md` | | Storage issues, files disappeared | See `skills/storage-diag.md` | | Storage management, disk pressure | See `skills/storage-management-ref.md` | | Keychain / secure credential storage | See axiom-security (skills/keychain.md) | | Keychain errors (errSecDuplicateItem) | See axiom-security (skills/keychain-diag.md) | | Keychain API reference | See axiom-security (skills/keychain-ref.md) | | Encryption / signing / key management | See axiom-security (skills/cryptokit.md) | | CryptoKit API reference | See axiom-security (skills/cryptokit-ref.md) | | File protection, NSFileProtection | See axiom-security (skills/file-protection-ref.md) | | tvOS data persistence (no local storage) | See axiom-swift (skills/tvos.md) | | tvOS + CloudKit SyncEngine | See `skills/sqlitedata.md` |

Automated Scanning

**Core Data audit** → `axiom-audit-core-data` (safety violations, architectural gaps — migration options, thread-confinement, N+1 queries, merge policies, context isolation) **Codable audit** → `axiom-audit-codable` (safety violations, semantic gaps — try? swallowing errors, JSONSerialization, date handling, silent field drops, wrapper-hidden fallbacks, cross-file strategy drift, enum future-case crashes) **iCloud audit** → `axiom-audit-icloud` (entitlement checks, file coordination, incomplete CKError matrix coverage, missing account-change observation, polling vs CKSubscriptions, SwiftData + CloudKit unsupported features, compound risks like uncoordinated I/O across extensions) **Storage audit** → `axiom-audit-storage` (wrong file locations, missing backup exclusions, sensitive data on disk vs Keychain, missing App Group containers, unbounded cache growth, orphan files, compound risks like user data in tmp/ + critical content) **Database schema audit** → `axiom-audit-database-schema` (unsafe ALTER TABLE, DROP operations, missing idempotency, FK constraints declared but not enforced, incomplete upgrade paths, compound risks like INSERT OR REPLACE on FK-referenced tables) **GRDB performance audit** → `axiom-audit-grdb-performance` (raw SQL string interpolation, missing FK indexes in raw SQL, missing PRAGMA optimize for raw-GRDB apps, journal mode mismatch for app-group DBs, missing observesSuspensionNotifications for shared DBs, prefix-redundant indexes in raw SQL, legacy Record subclass, INSERT OR REPLACE misused as upsert, observation on WITHOUT ROWID tables, WITHOUT ROWID upsert bugs) **SwiftData audit** → `axiom-audit-swiftdata` (struct models, missing schema registration, array relationships without defaults, background context misuse, N+1 patterns, stale predicates, CloudKit conformance gaps, co