swiftdata-architecture

Define @Model classes with relationship properties and choose delete rules: cascade for owned children, nullify for independent children, deny when children must be handled first. Add unique constraints with #Unique for natural keys like email to prevent duplicates.

Use @Query in SwiftUI views because it auto-updates when data changes. Use FetchDescriptor in ViewModels and services where you need pagination, fetchCount, identifier-only fetches, or background context execution.

SwiftData is recommended for new projects targeting macOS 14 or later, offering a Swift-native API with @Model macros and SwiftUI integration. Core Data remains relevant for older deployment targets or existing codebases.

Define a repository protocol returning DTOs instead of @Model types, implement it with a @ModelActor for SwiftData, and provide an in-memory actor implementation for tests. Inject the repository into ViewModels via initializer or SwiftUI environment.

Common causes are fetching all records without fetchLimit, materializing objects just to count them, and running heavy work on the main context. Use fetchCount, propertiesToFetch, pagination, and @ModelActor for background batch operations.

Not directly—models are bound to their ModelContext. Create a background ModelContext from the same container or use @ModelActor, re-fetch the model by identifier in that context, then modify and save there.