I've got a Classification model. And a TodoItem model , which has a attribute type Classification

@Model
final class Classification: Identifiable, Equatable {
    var id: UUID
    var image: String
    var background: Int
    var name: String

    init(id: UUID = UUID(), image: String, background: Int, name: String) {
        self.id = id
        self.image = image
        self.background = background
        self.name = name
    }

    static let mockData = Classification(image: "questionmark", background: 0xFF0000, name: "tag")
}

@Model
final class TodoItem: Identifiable {
    var id: UUID
    var title: String
    var startTime: Date
    var endTime: Date
    var isCompleted: Bool
    var isLog: Bool
    var classification: Classification?

    init(id: UUID = UUID(),  title: String, startTime: Date, endTime: Date, isCompleted: Bool, isLog: Bool, classification: Classification?) {
        self.id = id
        self.title = title
        self.startTime = startTime
        self.endTime = endTime
        self.isCompleted = isCompleted
        self.isLog = isLog
        self.classification = classification
    }

    convenience init(title: String, startTime: Date, endTime: Date, classification: Classification?) {
        self.init(id: UUID(), title: title, startTime: startTime, endTime: endTime, isCompleted: true, isLog: true, classification: classification)
    }

    static let mockDataTodo = TodoItem( title: "todo", startTime: Date(), endTime: Date(timeIntervalSinceNow: 3000), isCompleted: false, isLog: false, classification: nil)
    static let mockDataLog = TodoItem(title: "log", startTime: Date(timeIntervalSinceNow: -3000), endTime: Date(), classification: nil)
}

on my view ,when i create a todoItem , I need to choose classifications which stored in swiftData through a Picker

 @Query private var classifications: [Classification]
 @State private var todoItem: TodoItem

Picker("choose tag", selection: $selectedClassification) {
                Text("empty").tag(nil as Classification?)
                ForEach(classifications) { item in
                    TagView(classification: item)
                    .tag(Optional(item))
                }
            }
            .onChange(of: selectedClassification) { oldVlaue, newValue in
                if let newValue {
                    todoItem.classification = newValue
                } else {
                    todoItem.classification = nil
                }
            }

            CircleButton(imageString: "checkmark", width: 35, backgroundColor: .green, imageColor: .white,  ifGradient: true)
                    .onTapGesture {
                        withAnimation(.snappy) {
                            modelContext.insert(todoItem)
                            dismiss()
                        }
                    }

I got a CircleButton to execute modelContext.insert, but When I just picked classification, this todoItem will be stored immediately! I have no idea about this. But if I do not get classifications from swiftdata, but define a mock classifications myself, it will not be automatically inserted.

//    @Query private var classifications: [Classification]
    var classifications: [Classification] = [
        Classification(image: "checkmark", background: 0xff12df, name: "1"),
        Classification(image: "checkmark", background: 0xff12df, name: "2"),
        Classification(image: "checkmark", background: 0xff12df, name: "3"),
    ]