SwiftData/PersistentModel.swift:540：致命错误：不支持的关系键路径 ReferenceWritableKeyPath

Question

我有一对多关系 SwiftData 模型。但是，当我尝试附加数据时，会导致错误SwiftData/PersistentModel.swift:540: Fatal error: Unsupported relationship key path ReferenceWritableKeyPath<Student, School>。我应该如何解决这个问题？

@Model
final class School {
  var name: String
  @Relationship(deleteRule: .cascade, inverse: \Student.school)
  var students: [Student] = []

  init(name: String) {
    self.name = name
  }
}

@Model
final class Student {
  var fullName: String
  var school: School

  init(fullName: String, school: School) {
    self.fullName = fullName
    self.school = school
  }
}

struct AddStudentToSchoolView: View {
  let school: School
  @Environment(\.modelContext) private var modelContext

  var body: some View {
    // code ...
    Button("submit". action: { addStudentToSchool() })
  }
  
  private func addStudentToSchool() {
    let student = Student(fullName: "Jenny", school: self.school)
    modelContext.insert(student)
    self.school.students.append(student) // <- error SwiftData/PersistentModel.swift:540: Fatal error: Unsupported relationship key path ReferenceWritableKeyPath<Student, School>
  }
}

如果我注释掉self.school.students.append(student)一行，它工作正常，但是即使我删除一个学校，属于该学校的学生也不会作为级联删除被删除。我在苹果论坛上发现了类似的问题https://developer.apple.com/forums/thread/736908

Answer 1

即使您已经为学生分配了学校，您仍将学生追加到学校。

let student = Student(fullName: "Jenny", school: self.school)

SwiftData 将为您处理关系的另一端，因此将在 init中的students.append(student)行自动为您完成。self.school = schoolStudent

因此只需删除添加学生函数中的append()代码即可

private func addStudentToSchool() {
    let student = Student(fullName: "Jenny", school: self.school)
    modelContext.insert(student)
}