2nd/10_Wiki/Topics/Coding/iOS_SwiftData_Patterns.md

---
id: ios-swiftdata-patterns
title: SwiftData — Modern Persistence (iOS 17+)
category: Coding
status: draft
source_trust_level: B
verification_status: conceptual
created_at: 2026-05-09
updated_at: 2026-05-09
tags: [ios, swiftdata, persistence, vibe-coding]
tech_stack: { language: "Swift / SwiftData", applicable_to: ["iOS"] }
applied_in: []
aliases: [SwiftData, @Model, ModelContainer, ModelContext, query, predicate]
---

# SwiftData (iOS 17+)

> Core Data 의 현대적 wrapper. **`@Model` macro + Swift native syntax**. SwiftUI 통합. iCloud 동기화 자동. 새 프로젝트 = SwiftData.

## 📖 핵심 개념
- @Model: persisted class.
- ModelContainer: store.
- ModelContext: 변경 단위 (transaction).
- @Query: SwiftUI 자동 fetch.

## 💻 코드 패턴

### Model
```swift
import SwiftData

@Model
final class Note {
    @Attribute(.unique) var id: UUID
    var title: String
    var body: String
    var createdAt: Date
    
    @Relationship(deleteRule: .cascade) var tags: [Tag] = []
    
    init(title: String, body: String) {
        self.id = UUID()
        self.title = title
        self.body = body
        self.createdAt = Date()
    }
}

@Model
final class Tag {
    @Attribute(.unique) var name: String
    var notes: [Note] = []
    
    init(name: String) { self.name = name }
}
```

### App setup
```swift
@main
struct MyApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
        .modelContainer(for: [Note.self, Tag.self])
    }
}
```

### SwiftUI — @Query
```swift
struct NotesList: View {
    @Query(sort: \Note.createdAt, order: .reverse) private var notes: [Note]
    @Environment(\.modelContext) private var ctx
    
    var body: some View {
        List {
            ForEach(notes) { note in
                NavigationLink(value: note) {
                    Text(note.title)
                }
            }
            .onDelete(perform: delete)
        }
    }
    
    private func delete(at offsets: IndexSet) {
        for i in offsets {
            ctx.delete(notes[i])
        }
    }
}
```

### Filter (Predicate)
```swift
@Query(filter: #Predicate<Note> { $0.title.contains("Foo") },
       sort: \.createdAt, order: .reverse)
var notes: [Note]
```

```swift
// Dynamic
@Query private var notes: [Note]

init(searchText: String) {
    let predicate = #Predicate<Note> { $0.title.localizedStandardContains(searchText) }
    _notes = Query(filter: predicate, sort: \.createdAt, order: .reverse)
}
```

### CRUD
```swift
// Create
let note = Note(title: "Hello", body: "World")
ctx.insert(note)
try ctx.save()  // 또는 자동 (SwiftUI)

// Update — 그냥 변경
note.title = "Updated"
try ctx.save()

// Delete
ctx.delete(note)
try ctx.save()

// Fetch (manual)
let descriptor = FetchDescriptor<Note>(
    predicate: #Predicate { $0.title.contains("Foo") },
    sortBy: [SortDescriptor(\.createdAt, order: .reverse)]
)
let notes = try ctx.fetch(descriptor)
```

### Relationship
```swift
let note = Note(title: "...", body: "...")
let tag = Tag(name: "important")
note.tags.append(tag)
ctx.insert(note)
try ctx.save()
// tag 도 자동 insert
```

### Cascade delete
```swift
@Relationship(deleteRule: .cascade) var tags: [Tag]
// note 삭제 = tags 도

@Relationship(deleteRule: .nullify) var author: User?
// note 삭제 = user.notes 에서 nullify
```

### iCloud sync (CloudKit)
```swift
.modelContainer(for: Note.self, isAutosaveEnabled: true)

// Cloud 자동 sync — Bundle ID + iCloud capability + entitlement
```

```
Capabilities → iCloud → CloudKit
+ Background Modes → Remote notifications
```

→ 사용자가 iCloud 계정만 있으면 자동.

### Migration
```swift
enum NotesV1: VersionedSchema {
    static var versionIdentifier = Schema.Version(1, 0, 0)
    static var models: [any PersistentModel.Type] = [Note.self]
}

enum NotesV2: VersionedSchema {
    static var versionIdentifier = Schema.Version(2, 0, 0)
    static var models: [any PersistentModel.Type] = [Note.self]
}

enum MigrationPlan: SchemaMigrationPlan {
    static var schemas: [any VersionedSchema.Type] = [NotesV1.self, NotesV2.self]
    static var stages: [MigrationStage] = [
        .lightweight(fromVersion: NotesV1.self, toVersion: NotesV2.self),
    ]
}

let container = try ModelContainer(
    for: Note.self,
    migrationPlan: MigrationPlan.self
)
```

### Background context
```swift
let context = ModelContext(container)
// 또는 동기 — main actor 권장 SwiftUI

// Heavy import
Task.detached {
    let bgContext = ModelContext(container)
    for item in items {
        bgContext.insert(...)
    }
    try bgContext.save()
}
```

### vs Core Data
```
SwiftData:
+ 코드 단순, type-safe
+ macro 자동
+ Async/await 친화
- iOS 17+ only
- 일부 advanced 기능 부족 (NSPredicate 만큼)

Core Data:
+ 안정 / 강력
+ 모든 OS
- Boilerplate
- Objc legacy
```

→ 새 프로젝트 + iOS 17+ = SwiftData.

### Performance 팁
- @Query 자동 throttle (UI 안 깨짐).
- Predicate 안 무거운 계산 X.
- 큰 fetch = sortBy / fetchLimit.
- Background context 큰 import.

```swift
let descriptor = FetchDescriptor<Note>()
descriptor.fetchLimit = 50
descriptor.fetchOffset = page * 50
```

### Error handling
```swift
do {
    try ctx.save()
} catch {
    log.error("save failed: \(error)")
    ctx.rollback()
}
```

## 🤔 의사결정 기준
| 상황 | 추천 |
|---|---|
| iOS 17+ 새 프로젝트 | SwiftData |
| 기존 Core Data | Core Data 유지 또는 점진 |
| 매우 단순 | UserDefaults / file |
| 큰 / 복잡 query | Core Data + NSFetchRequest |
| Cross-platform (Android) | SQLite + SQLDelight |
| Cloud sync 필요 | SwiftData + CloudKit |

## ❌ 안티패턴
- **Main thread 큰 import**: UI freeze. background context.
- **@Query 너무 많은 row**: limit / pagination.
- **Predicate 안 비싼 함수**: 매 row evaluation.
- **save() 매 변경**: batch.
- **Migration 무계획**: production data 손실.
- **Core Data + SwiftData 같은 store**: 헷갈림. 한 가지.
- **Schema 변경 + lightweight 가정**: 복잡 = custom migration.

## 🤖 LLM 활용 힌트
- @Model + @Query + ModelContext 3종.
- SwiftUI 자동 통합 = 재렌더 자동.
- Migration plan 명시.
- iCloud 자동 sync — capability 켜기.

## 🔗 관련 문서
- [[iOS_Core_Data_Patterns]]
- [[iOS_Swift_Macros]]
- [[iOS_SwiftUI_State_Property_Wrappers]]