在 SwiftData 中，我不断收到错误“这里不允许使用 userInfo of (null) 的对多键”，并且无法解决问题

Question

我有以下 SwiftData 模型，并正在尝试为它们编写单元测试。我可以检索数据并筛选非关系属性。不幸的是，这不适用于关系属性，我总是收到错误消息“错误：SQLCoredispatchRequest：异常处理请求：

<NSSQLFetchRequestContext: 0x600003b3ff00> , to-many key not allowed here with userInfo of (null)

我已经尝试解决这个问题好几天了，但不幸的是没有成功。 我想检索输入学生“Bob”的所有课程。有人可以帮助我并解释我做错了什么

@Model
public final class StudentModel {
    
    public var name: String?
    
    @Relationship(inverse: \ClassModel.students)
    public var classes: [ClassModel]?
    
    public init(
        name: String
    ) {
        self.name = name
    }
}

@Model
public final class ClassModel {
    
    public var subject: String?
    public var students: [StudentModel]?
    
    public init(
        subject: String,
        students: [StudentModel] = []
    ) {
        self.subject = subject
        self.students = students
    }
}

final class ClassesAndStudents: XCTestCase {
    
    private var modelContainer: ModelContainer? = {
        let modelConfiguration = ModelConfiguration(isStoredInMemoryOnly: true)
        do {
            return try ModelContainer(
                for: ClassModel.self,
                configurations: modelConfiguration
            )
        }
        catch {
            XCTFail("Could not create ModelContainer: \(error)")
            return nil
        }
    }()

    @MainActor
    func testManyToManyFetch() throws {
        let sut = self.modelContainer!.mainContext
        
        let studentsA = [
            StudentModel(name: "Susan"),
            StudentModel(name: "Bob"),
            StudentModel(name: "Josie"),
        ]
        
        let studentsB = [
            StudentModel(name: "Susan"),
            StudentModel(name: "Josie"),
        ]
        
        let mathClass = ClassModel(
            subject: "Math",
            students: studentsA
        )
        sut.insert(mathClass)
        
        let biologyClass = ClassModel(
            subject: "Biology",
            students: studentsB
        )
        sut.insert(biologyClass)
            
        do {
            let descriptor = FetchDescriptor<ClassModel>(predicate: #Predicate {
                $0.students.flatMap { $0.contains { $0.name == "Bob" } } ?? false
            })
            let classes = try sut.fetch(descriptor) // ERROR: SQLCore dispatchRequest: exception handling request: <NSSQLFetchRequestContext: 0x600003b46840> , to-many key not allowed here with userInfo of (null)
            XCTAssertEqual(classes.count, 1, "There should be 1 class from fetch")
        }
        catch {
            XCTFail("Fetch failed: \(error)")
        }
    }
}

Answer 1

Joakim Danielson 的回答对我有帮助：

@MainActor
func testManyToManyFetch() throws {
    let sut = self.modelContainer!.mainContext
    
    let studentsA = [
        StudentModel(name: "Susan"),
        StudentModel(name: "Bob"),
        StudentModel(name: "Josie"),
    ]
    
    let studentsB = [
        StudentModel(name: "Susan"),
        StudentModel(name: "Josie"),
    ]
    
    let mathClass = ClassModel(
        subject: "Math",
        students: studentsA
    )
    sut.insert(mathClass)
    
    let biologyClass = ClassModel(
        subject: "Biology",
        students: studentsB
    )
    sut.insert(biologyClass)
        
    do {
        let descriptor = FetchDescriptor<StudentModel>(predicate: #Predicate { $0.name == "Bob" })
        let classes = try sut.fetch(descriptor).map(\.classes)
        XCTAssertEqual(classes.count, 1, "There should be 1 class from fetch")
    }
    catch {
        XCTFail("Fetch failed: \(error)")
    }
}