使用CoreData在SwiftUI中创建供应商并为其添加品牌

import SwiftUI
import CoreData

// Supplier实体对应的NSManagedObject子类
class Supplier: NSManagedObject {
    @NSManaged var name: String
    @NSManaged var brands: NSSet?
}

// Brand实体对应的NSManagedObject子类
class Brand: NSManagedObject {
    @NSManaged var name: String
    @NSManaged var supplier: Supplier?
}

struct ContentView: View {
    @Environment(\.managedObjectContext) private var viewContext
    @FetchRequest(entity: Supplier.entity(), sortDescriptors: []) var suppliers: FetchedResults<Supplier>

    var body: some View {
        NavigationView {
            List {
                ForEach(suppliers, id: \.self) { supplier in
                    NavigationLink(destination: BrandListView(supplier: supplier)) {
                        Text(supplier.name ?? "")
                    }
                }
            }
            .toolbar {
                ToolbarItem(placement: .navigationBarTrailing) {
                    Button(action: addSupplier) {
                        Label("Add Supplier", systemImage: "plus")
                    }
                }
            }
        }
    }

    private func addSupplier() {
        let supplier = Supplier(context: viewContext)
        supplier.name = "New Supplier"
        do {
            try viewContext.save()
        } catch {
            let nsError = error as NSError
            fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
        }
    }
}

struct BrandListView: View {
    @ObservedObject var supplier: Supplier
    @Environment(\.managedObjectContext) private var viewContext

    var body: some View {
        List {
            ForEach(supplier.brands?.allObjects as? [Brand] ?? [], id: \.self) { brand in
                Text(brand.name ?? "")
            }
        }
        .toolbar {
            ToolbarItem(placement: .navigationBarTrailing) {
                Button(action: addBrand) {
                    Label("Add Brand", systemImage: "plus")
                }
            }
        }
    }

    private func addBrand() {
        let brand = Brand(context: viewContext)
        brand.name = "New Brand"
        brand.supplier = supplier
        do {
            try viewContext.save()
        } catch {
            let nsError = error as NSError
            fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
        }
    }
}