Swift Data

SwiftData

You are a SwiftData expert. Apply these patterns when working with data persistence in Swift apps.

When to Use

• Adding persistence to SwiftUI apps
• Defining data models with relationships
• Querying and filtering data
• Syncing with iCloud/CloudKit
• Migrating from Core Data

Decision Tree

| Need | Reference | |------|-----------| | Define models and properties | → [model-basics.md](references/model-basics.md) | | Create relationships between models | → [relationships.md](references/relationships.md) | | Query, filter, and sort data | → [queries-filtering.md](references/queries-filtering.md) | | Configure containers and contexts | → [containers-contexts.md](references/containers-contexts.md) | | Enable iCloud sync | → [cloudkit-sync.md](references/cloudkit-sync.md) | | Handle schema migrations | → [migration.md](references/migration.md) | | Optimize performance | → [performance.md](references/performance.md) | | Debug and troubleshoot | → [common-issues.md](references/common-issues.md) |

Core Principles

1. Use @Model for all persistent types - Classes only, not structs
2. Relationships must be optional or have defaults - For CloudKit compatibility
3. ModelContext is thread-bound - Never pass contexts between threads
4. Prefer @Query in SwiftUI - Automatic updates when data changes
5. Autosave is on by default - Changes persist automatically

Quick Reference

Basic Model

import SwiftData

@Model
final class Book {
    var title: String
    var author: String
    var publishedDate: Date
    var rating: Int?

    init(title: String, author: String, publishedDate: Date) {
        self.title = title
        self.author = author
        self.publishedDate = publishedDate
    }
}

App Setup

@main
struct MyApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
        .modelContainer(for: Book.self)
    }
}

Query in SwiftUI

struct BookList: View {
    @Query(sort: \Book.title) var books: [Book]
    @Environment(\.modelContext) var modelContext

    var body: some View {
        List(books) { book in
            Text(book.title)
        }
    }
}

CRUD Operations

// Create
let book = Book(title: "Swift Guide", author: "Apple", publishedDate: .now)
modelContext.insert(book)

// Read - use @Query or fetch
let descriptor = FetchDescriptor(
    predicate: #Predicate { $0.rating ?? 0 > 3 },
    sortBy: [SortDescriptor(\.title)]
)
let books = try modelContext.fetch(descriptor)

// Update - modify properties directly
book.title = "Updated Title"

// Delete
modelContext.delete(book)

Note

For comprehensive SwiftData tutorials, check Hacking with Swift - SwiftData.

References

• [model-basics.md](references/model-basics.md) - @Model macro, properties, attributes
• [relationships.md](references/relationships.md) - One-to-one, one-to-many, many-to-many
• [queries-filtering.md](references/queries-filtering.md) - @Query, predicates, sorting
• [containers-contexts.md](references/containers-contexts.md) - ModelContainer, ModelContext, configuration
• [cloudkit-sync.md](references/cloudkit-sync.md) - iCloud sync setup and constraints
• [migration.md](references/migration.md) - Lightweight and complex migrations
• [performance.md](references/performance.md) - Batch operations, background contexts
• [common-issues.md](references/common-issues.md) - Debugging and troubleshooting

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: onmyway133
• Source: onmyway133/skills
• License: MIT
• Homepage: https://onmyway133.com

Install and usage instructions live in the source repository linked above.