# Ha IOS Persistence

> Data persistence across GRDB, Realm, and UserDefaults. Use when adding or migrating a persistent model, choosing a storage layer, implementing DatabaseTableProtocol, or reading/writing config for Watch, CarPlay, widgets, or the entity registry.

- Skill: `home-assistant/ha-ios-persistence` (Agent Skill)
- Install (CLI): `npx skillmds@latest add home-assistant/ha-ios-persistence`
- Raw SKILL.md: https://api.skillmd.com/api/skills/home-assistant/ha-ios-persistence/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: home-assistant (https://skillmd.com/u/home-assistant)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/home-assistant/ha-ios-persistence

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# Data Persistence

The project uses **two** database layers:

- **GRDB** (`GRDB.swift`): newer layer, accessed via `Current.database()`. Used for Watch config, CarPlay config, widget config, entity registry, panels, etc. When adding a new persistent model, prefer GRDB: implement `DatabaseTableProtocol` (defines `tableName`, `definedColumns`, and `createIfNeeded`) and register it in `DatabaseQueue.tables()` in `GRDB+Initialization.swift`. The protocol's `migrateColumns` helper auto-handles additive migrations.
- **Realm** (`RealmSwift`): legacy layer, used for older models (actions, zones, sensors, etc.). Access via `Current.realm()`.
- **UserDefaults**: simple preferences and watch communication.