Swift数据建模和保存不可为 null 的关系-解网

问：

我有以下代码：

import SwiftUI
import SwiftData

struct ContentView: View {
    @Environment(\.modelContext) private var modelContext

    var schoolClass: SchoolClass

    var body: some View {
        VStack {
            Image(systemName: "globe")
                .imageScale(.large)
                .foregroundStyle(.tint)
            Text("Hello, world!")
            Button("add", action: {
                let schoolClassSubject = SchoolClassSubject(schoolClass: schoolClass)
                schoolClass.schoolClassSubjects.append(schoolClassSubject)
            })
            
        }
        .padding()
    }
}

@Model
class SchoolClass {
    var name: String
    var schoolClassSubjects: [SchoolClassSubject] = []
    
    init(name: String) {
        self.name = name
    }
}

@Model
class SchoolClassSubject {
    var schoolClass: SchoolClass
    
    init(schoolClass: SchoolClass) {
        print("test")
        self.schoolClass = schoolClass
    }
}

schoolClass已保存在 swiftData 中，并作为属性传递给。ContentView

换行符，但出现以下异常：let schoolClassSubject = SchoolClassSubject(schoolClass: schoolClass)

由于未捕获的异常“NSInvalidArgumentException”而终止应用，原因：“非法尝试在不同上下文中的对象之间建立关系”schoolClass“（源 = <NSManagedObject：0x60000214cc30>（实体：SchoolClassSubject;id：0x60000024ebe0 x-coredata：///SchoolClassSubject/t186670BB-357C-400C-8D6F-178BEB8F4B473;数据：{ schoolClass = nil;}），目标 = <NSManagedObject：0x60000214cd70>（实体：SchoolClass;id：0x600000276740 x-coredata：学校班级/t186670BB-357C-400C-8D6F-178BEB8F4B472;data： { name = test; schoolClassSubjects = （）; }））'第一次抛出呼叫

如果我将我的模型更改为：

@Model
class SchoolClassSubject {
    var schoolClass: SchoolClass? = nil
    init() {
    }
}

我的保存代码如下：

let schoolClassSubject = SchoolClassSubject()
modelContext.insert(schoolClassSubject)
schoolClassSubject.schoolClass = schoolClass
schoolClass.schoolClassSubjects.append(schoolClassSubject)

但我不想做可选，因为它不是现实。我怎样才能使它不是可选的，并且仍然保存它而不会出现给定的错误？schoolClassschoolClassSubject

SwiftUI Swift-Data

Think it depends on how to keep track of your RelationShip.
If One To Many Relation.

SchoolClass kan have many SchoolClassSubject
SchoolClassSubject only belong to one SchoolClass

@Model
class SchoolClass {
    var name: String
     @Relationship(deleteRule: .cascade)
     var schoolClassSubjects =[SchoolClassSubject]() 
    init(name: String) {
        self.name = name
    }
}

@Model
class SchoolClassSubject {
    var schoolClassSubject: String

    @Relationship(inverse: \SchoolClass.schoolClassSubjects)
    var schoolClass: SchoolClass?  // ? meaning of optional 


    init(schoolClassSubject: String) {
        //print("test")
        self.schoolClassSubject = schoolClassSubject
    }
}
// then in WindowGroup you have to have
 .modelContainer(for: SchoolClass .self

//In Views
 @Environment(\.modelContext) private var context
    
    let schoolClass: SchoolClass

// You can do in Views save func
let transaction = SchoolClassSubject(schoolClassSubject: "String here..")

transaction.schoolClass = schoolClass

Swift数据建模和保存不可为 null 的关系

SwiftData Modeling and saving non Nullable Relations

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