65 lines
2.0 KiB
Markdown
65 lines
2.0 KiB
Markdown
# LocalData Migration Guide
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## Overview
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`LocalData` provides protocol-based migration support to move data from legacy storage locations to modern `StorageKey` definitions.
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## Automatic Migration
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When calling `get(_:)` on a key, the `StorageRouter` automatically:
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1. Checks the primary location.
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2. If not found, evaluates `migration` defined on the key.
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3. If data is found in a source:
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- Unsecures it using the source's old policy.
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- Re-secures it using the destination key's policy.
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- Stores it in the new location.
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- Deletes the legacy data.
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- Returns the value.
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## Proactive Migration (Sweep)
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You can trigger a sweep of all registered keys at app launch:
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```swift
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try await StorageRouter.shared.registerCatalog(MyCatalog(), migrateImmediately: true)
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```
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This iterates through all keys in the catalog and calls `forceMigration(for:)` on each, ensuring all legacy data is consolidated.
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## Defining Migration Sources
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### Simple Legacy Migration
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For 1:1 migrations, attach a `SimpleLegacyMigration`:
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```swift
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struct MyNewKey: StorageKey {
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// ...
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var migration: AnyStorageMigration? {
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AnyStorageMigration(
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SimpleLegacyMigration(
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destinationKey: self,
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sourceKey: .key(LegacyKey(name: "old_key_name", domain: .userDefaults(suite: nil)))
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)
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)
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}
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}
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```
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### Protocol-Based Migration
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For complex scenarios, attach an explicit migration:
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```swift
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struct MyMigration: StorageMigration {
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typealias DestinationKey = MyNewKey
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let destinationKey = MyNewKey()
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func shouldMigrate(using router: StorageRouter, context: MigrationContext) async throws -> Bool {
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try await router.exists(destinationKey)
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}
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func migrate(using router: StorageRouter, context: MigrationContext) async throws -> MigrationResult {
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// Custom migration logic
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MigrationResult(success: true)
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}
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}
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extension MyNewKey {
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var migration: AnyStorageMigration? {
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AnyStorageMigration(MyMigration())
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}
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}
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```
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