使用 SwiftData 为你的架构建模

0:56 - Original Trip model

import SwiftUI
import SwiftData

@Model
final class Trip {
    var name: String
    var destination: String
    var start_date: Date
    var end_date: Date
    
    var bucketList: [BucketListItem]? = []
    var livingAccommodation: LivingAccommodation?
}

1:50 - Adding a unique attribute

@Model 
final class Trip {
    @Attribute(.unique) var name: String
    var destination: String
    var start_date: Date
    var end_date: Date
    
    var bucketList: [BucketListItem]? = []
    var livingAccommodation: LivingAccommodation?
}

2:48 - Specifying original property names

@Model 
final class Trip {
    @Attribute(.unique) var name: String
    var destination: String
    @Attribute(originalName: "start_date") var startDate: Date
    @Attribute(originalName: "end_date") var endDate: Date
    
    var bucketList: [BucketListItem]? = []
    var livingAccommodation: LivingAccommodation?
}

4:00 - Cascading delete rule

@Model 
final class Trip {
    @Attribute(.unique) var name: String
    var destination: String
    @Attribute(originalName: "start_date") var startDate: Date
    @Attribute(originalName: "end_date") var endDate: Date
    
    @Relationship(.cascade)
    var bucketList: [BucketListItem]? = []
  
    @Relationship(.cascade)
    var livingAccommodation: LivingAccommodation?
}

4:54 - Transient properties

@Model 
final class Trip {
    @Attribute(.unique) var name: String
    var destination: String
    @Attribute(originalName: "start_date") var startDate: Date
    @Attribute(originalName: "end_date") var endDate: Date
    
    @Relationship(.cascade)
    var bucketList: [BucketListItem]? = []
  
    @Relationship(.cascade)
    var livingAccommodation: LivingAccommodation?

    @Transient
    var tripViews: Int = 0
}

7:12 - Defining versioned schemas

enum SampleTripsSchemaV1: VersionedSchema {
    static var models: [any PersistentModel.Type] {
        [Trip.self, BucketListItem.self, LivingAccommodation.self]
    }

    @Model
    final class Trip {
        var name: String
        var destination: String
        var start_date: Date
        var end_date: Date
    
        var bucketList: [BucketListItem]? = []
        var livingAccommodation: LivingAccommodation?
    }

    // Define the other models in this version...
}

enum SampleTripsSchemaV2: VersionedSchema {
    static var models: [any PersistentModel.Type] {
        [Trip.self, BucketListItem.self, LivingAccommodation.self]
    }

    @Model
    final class Trip {
        @Attribute(.unique) var name: String
        var destination: String
        var start_date: Date
        var end_date: Date
    
        var bucketList: [BucketListItem]? = []
        var livingAccommodation: LivingAccommodation?
    }

    // Define the other models in this version...
}

enum SampleTripsSchemaV3: VersionedSchema {
    static var models: [any PersistentModel.Type] {
        [Trip.self, BucketListItem.self, LivingAccommodation.self]
    }

    @Model
    final class Trip {
        @Attribute(.unique) var name: String
        var destination: String
        @Attribute(originalName: "start_date") var startDate: Date
        @Attribute(originalName: "end_date") var endDate: Date
    
        var bucketList: [BucketListItem]? = []
        var livingAccommodation: LivingAccommodation?
    }

    // Define the other models in this version...
}

7:49 - Implementing a SchemaMigrationPlan

enum SampleTripsMigrationPlan: SchemaMigrationPlan {
    static var schemas: [any VersionedSchema.Type] {
        [SampleTripsSchemaV1.self, SampleTripsSchemaV2.self, SampleTripsSchemaV3.self]
    }
    
    static var stages: [MigrationStage] {
        [migrateV1toV2, migrateV2toV3]
    }

    static let migrateV1toV2 = MigrationStage.custom(
        fromVersion: SampleTripsSchemaV1.self,
        toVersion: SampleTripsSchemaV2.self,
        willMigrate: { context in
            let trips = try? context.fetch(FetchDescriptor<SampleTripsSchemaV1.Trip>())
                      
            // De-duplicate Trip instances here...
                      
            try? context.save() 
        }, didMigrate: nil
    )
  
    static let migrateV2toV3 = MigrationStage.lightweight(
        fromVersion: SampleTripsSchemaV2.self,
        toVersion: SampleTripsSchemaV3.self
    )
}

8:40 - Configuring the migration plan

struct TripsApp: App {
    let container = ModelContainer(
        for: Trip.self, 
        migrationPlan: SampleTripsMigrationPlan.self
    )
    
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
        .modelContainer(container)
    }
}