Swift Data Fail to previewivrelationship

Hi! I was trying to develop a todo list app. There are two models:

import Foundation
import SwiftData

@Model
class Item {
    var id: UUID
    var title: String
    var detail: String
    @Relationship(deleteRule: .cascade, inverse: \SubItem.item) var subitems: [SubItem]
    
    var isCompleted: Bool
    var timestamp: Date
    
    init(id: UUID = UUID(), title: String = "", detail: String = "", subitems: [SubItem] = [], isCompleted: Bool = false, timestamp: Date = .now) {
        self.id = id
        self.title = title
        self.detail = detail
        self.subitems = subitems
        self.isCompleted = isCompleted
        self.timestamp = timestamp
    }
}

@Model
class SubItem {
    var id: UUID
    var title: String
    var isCompleted: Bool
    
    var item: Item
    
    init(id: UUID = UUID(), title: String = "", isCompleted: Bool = false, item: Item) {
        self.id = id
        self.title = title
        self.isCompleted = isCompleted
        self.item = item
    }
}

In a component view, I was trying to preload some sample data in the preview:

struct ItemRowView: View {
    @Bindable var item: Item
    //......
}

#Preview {
    let schema = Schema([
        Item.self,
        SubItem.self
    ])
    let modelConfiguration = ModelConfiguration(schema: schema, isStoredInMemoryOnly: true)
    let container = try! ModelContainer(for: schema, configurations: [modelConfiguration])
    let context = container.mainContext
    
    var item: Item = Item(title: "Item title 1", detail: "")
    var subitem1 = SubItem(title: "subitem 4", item: item)
    var subitem2 = SubItem(title: "subitem 2", item: item)
    
    context.insert(item)
    context.insert(subitem1)
    context.insert(subitem2)
    
    return ItemRowView(item: item)
        .modelContainer(container)
        .padding()
}

However, item.subitems is always empty in this view. What's wrong?