swiftdata

SwiftData (iOS 17+)

Overview

SwiftData is Apple's modern persistence framework (iOS 17+), built on Core Data but Swift-native. You declare models with the @Model macro; a ModelContainer holds the store, a ModelContext performs inserts/updates/deletes, and @Query drives SwiftUI views reactively.

When to use

• Local persistence in a native iOS app (iOS 17+)
• SwiftUI-driven, reactive data display
• Migrating from Core Data to a Swift-native API
• NOT for code shared with Android → use sqldelight-patterns

Model

import SwiftData

@Model
final class Plant {                          // must be a final class, not a struct
    @Attribute(.unique) var id: UUID
    var name: String
    var plantedOn: Date
    @Relationship(deleteRule: .cascade) var waterings: [Watering] = []

    init(name: String, plantedOn: Date = .now) {
        self.id = UUID(); self.name = name; self.plantedOn = plantedOn
    }
}

Container (app entry)

@main
struct GardenApp: App {
    var body: some Scene {
        WindowGroup { ContentView() }
            .modelContainer(for: Plant.self)   // creates the ModelContainer + store
    }
}

Query + mutate in a view

struct PlantList: View {
    @Environment(\.modelContext) private var context
    @Query(sort: \Plant.plantedOn, order: .reverse) private var plants: [Plant]

    var body: some View {
        List(plants) { Text($0.name) }
        Button("Add") { context.insert(Plant(name: "Fern")) }   // autosaved
    }
}

// Filtered query with a type-safe predicate
@Query(filter: #Predicate<Plant> { $0.name.contains("Fern") })
private var ferns: [Plant]

Explicit delete/save:

context.delete(plant)
try context.save()        // usually autosaved; call when you need it deterministic

Common mistakes

Mistake	Fix
Forgetting .modelContainer(...)	Without it @Query / modelContext have no store
Using NSPredicate	Use the type-safe #Predicate<T> { … }
Heavy writes on the main context	Use a separate ModelContext / @ModelActor off the main actor
@Model on a struct	@Model requires a final class
Targeting below iOS 17	SwiftData is iOS 17+; fall back to core-data