Storage Guide

Navigation hub for ALL storage decisions — where to store data, which technology to use, local vs cloud.

Overview

Comprehensive decision framework integrating SwiftData (WWDC 2023), CKSyncEngine (WWDC 2023), file management, and cloud sync. Guides developers to the right storage solution based on data shape and requirements.

What This Skill Covers

Storage Decision Framework

Structured Data Path

• Modern apps (iOS 17+) → SwiftData
• Advanced control → SQLiteData/GRDB
• Legacy apps → Core Data
• Cloud sync → SwiftData + CloudKit or CKSyncEngine

File Storage Path

• User-created content → Documents/
• App data (not visible) → Application Support/
• Re-downloadable → Caches/
• Temporary → tmp/

Cloud Storage Path

• Structured data → CloudKit (via SwiftData or CKSyncEngine)
• Files → iCloud Drive (ubiquitous containers)
• Small preferences → NSUbiquitousKeyValueStore

Cross-References

Database Skills:

• axiom-swiftdata — Modern persistence (iOS 17+)
• axiom-sqlitedata — Advanced SQLite control
• axiom-grdb — Reactive queries, migrations

File Skills:

• axiom-file-protection-ref — Encryption, security
• axiom-storage-management-ref — Purging, disk space
• axiom-storage-diag — Debug file issues

Cloud Skills:

• axiom-cloudkit-ref — Database sync
• axiom-icloud-drive-ref — File sync
• axiom-cloud-sync-diag — Debug sync issues

Common Patterns

Pattern: Choosing Storage Format

What are you storing?

STRUCTURED DATA (queryable, relationships)
→ SwiftData (modern, iOS 17+)
→ See: swiftdata skill

FILES (documents, images, caches)
→ FileManager + proper directory
→ See: file-protection-ref, storage-management-ref

Pattern: Local vs Cloud

Needs to sync across devices?

NO → Local storage
YES → Cloud storage
  - Structured data? → CloudKit (cloudkit-ref)
  - Files? → iCloud Drive (icloud-drive-ref)

Anti-Pattern: Wrong Format

❌ WRONG: JSON files for queryable data
→ Can't query, filter, or sort efficiently
→ FIX: Use SwiftData instead

❌ WRONG: Re-downloadable content in Documents/
→ Bloats backup
→ FIX: Use Caches/ with isExcludedFromBackup

Quick Decision Table

Data Type	Format	Local Location	Cloud	Related Skill
User tasks	Structured	App Support	SwiftData + CloudKit	swiftdata, cloudkit-ref
User photos	File	Documents	iCloud Drive	file-protection-ref, icloud-drive-ref
Downloaded images	File	Caches	None	storage-management-ref
Thumbnails	File	Caches	None	storage-management-ref
Preferences	Key-Value	UserDefaults	NSUbiquitousKVStore	N/A

Use This Skill When

• Starting new project (choosing storage approach)
• Asking "where should I store this data?"
• Deciding between SwiftData, files, or cloud
• Planning data architecture
• Migrating storage solutions

Related: Getting Started guide, swiftdata, cloudkit-ref, file-protection-ref