使实体关系可编码/可解码时出错

Question

如何在与 coredata NSManagedObject 映射时编码/解码 swift4 codable 中的 NSOrderedSet 变量？

import CoreData
import Foundation

@objc(TestObject)
public class TestObject:NSManagedObject,Encodable
{

@nonobjc public class func fetchRequest() -> NSFetchRequest<TestObject> {
    return NSFetchRequest<TestObject>(entityName: "TestObject")
}


@NSManaged public var testName: String?
@NSManaged public var devices: NSOrderedSet?  // of entity type "Device"

enum CodingKeys: String, CodingKey {
    case testName
    case devices

}
public func encode(to encoder: Encoder) throws {
     var container = encoder.container(keyedBy:CodingKeys.self)
    try container.encode(testName,forKey:.testName)
    try container.encode(devices,forKey:.devices)
}
}

public required convenience init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
    try container.decode(testName,forKey:.testName)
    try container.decode(devices,forKey:.devices)

}

它给出错误：编译器给出了这个错误

No 'decode' candidates produce the expected contextual result type 'NSOrderedSet?'

Answer 1

您可以通过利用自动生成的访问器之一来做到这一点。

//addToDevices(_ value: Device) 

public required convenience init(from decoder: Decoder) throws {
    let container = try decoder.container(keyedBy: CodingKeys.self)
    self.testName = try container.decode(String.self, forKey: .testName)
    let devices = try container.decode([Device].self, forKey:.devices)
    devices.forEach { self.addToDevices($0) }
}

如果您没有自动生成的访问器，请按照以下步骤操作

1. 选择您的项目数据模型文件
2. 选择菜单栏苹果左起第7个“编辑器”
3. 选择“创建 NSManagedObject 子类
4. 选中数据模型旁边的框
5. 选中您要使用的实体的框
6. 选择“创建”