如何从json解析为Core Data模型，那里有一个带有关联值的枚举？

如何解决如何从json解析为Core Data模型，那里有一个带有关联值的枚举？

型号

struct UserList {

    var privacy: Access
    var sharing: Access
}

enum Access: {

    case `private`
    case friendsOnly
    case someFriends(ids: [String])
    case `public`
} 

CoreData模型

@objc(UserListModel)
public class UserListModel: NSManagedObject {
    @NSManaged public var privacy: AccessModel
    @NSManaged public var sharing: AccessModel
    @NSManaged public var someFriendsPrivacy: SomeFriendsPrivacyModel?
    @NSManaged public var someFriendsSharing: SomeFriendsSharingModel?
}

@objc(SomeFriendsSharingModel)
public class SomeFriendsSharingModel: NSManagedObject {
    @NSManaged public var ids: [String]
    @NSManaged public var userList: UserListModel
}

@objc public enum AccessModel: Int32 {

    case `public` = 0
    case friendsOnly = 1
    case someFriends = 2
    case `private` = 3

}

CoreData设置：

this thread

问题：

1. 如何将Codable添加到UserList以从json获取模型？

{"privacy":"friendsOnly","sharing":{
    "some_friends":
          {"ids":["id1","id2"]}
    }
}

1. 如何将可编码添加到核心数据模型？为了能够将模型从json直接保存到Core Data？
2. 如何从Core Data UserListModel初始化UserList模型？

解决方法

1. 如何将Codable添加到UserList以从json获取模型？

extension UserList: Codable {}

enum AccessCodableError: Error {
    case error(String)
}

extension Access: Codable {

    enum CodingKeys: String,CodingKey {
        case someFriends
    }

    enum NestedKeys: String,CodingKey {
        case ids
    }

    var rawValue: String {
        switch self {
        case .friendsOnly:
            return "friendsOnly"
        case .private:
            return "private"
        case .public:
            return "public"
        case .someFriends:
            return "someFriends"
        }
    }

    init(from decoder: Decoder) throws {
        if let container = try? decoder.container(keyedBy: CodingKeys.self) {
            let nestedContainer = try container.nestedContainer(keyedBy: NestedKeys.self,forKey: .someFriends)
            let ids = try nestedContainer.decode([String].self,forKey: .ids)
            self = .someFriends(ids: ids)
        }
        else {
            let container = try decoder.singleValueContainer()
            let accessValue = try container.decode(String.self)
            switch accessValue {
            case let value where value == Access.private.rawValue:
                self = .private
            case let value where value == Access.friendsOnly.rawValue:
                self = .friendsOnly
            case let value where value == Access.public.rawValue:
                self = .public

            default:
                throw AccessCodableError.error("Can't determine the decodable key")
            }
        }

    }

    func encode(to encoder: Encoder) throws {
        switch self {
        case .private,.friendsOnly,.public:
            var container = encoder.singleValueContainer()
            try container.encode(self.rawValue)
        case .someFriends(let userIds):
            var container = encoder.container(keyedBy: CodingKeys.self)

            var nestedContainer = container.nestedContainer(keyedBy: NestedKeys.self,forKey: .someFriends)
            try nestedContainer.encode(userIds,forKey: .ids)
        }
    }

}

用法（例如，不安全）：

// Encode
let userList1 = UserList(privacy: .friendsOnly,sharing: .someFriends(ids: ["id1","id2"]))
let encoder = JSONEncoder()
encoder.keyEncodingStrategy = .convertToSnakeCase
let json = try! encoder.encode(userList1) 
// Decode
let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase
let decodedList = try! decoder.decode(UserList.self,from: json)

1. 如何将可编码添加到核心数据模型？为了能够将模型从json直接保存到Core Data？

extension Access {
    var ids: [String]? {
        switch self {
        case .someFriends(let ids):
            return ids
        default:
            return nil
        }
    }
}

extension CodingUserInfoKey {
    static let context = CodingUserInfoKey(rawValue: "context")!
}

@objc(UserListModel)
public class UserListModel: NSManagedObject,Decodable {

    enum CodingKeys: String,CodingKey {
        case privacy
        case sharing
    }

    required convenience public init(from decoder: Decoder) throws {
        guard let context = decoder.userInfo[.context] as? NSManagedObjectContext
            else { throw NSError() }
        self.init(context: context)
        let container = try decoder.container(keyedBy: CodingKeys.self)
        let privacy = try container.decode(Access.self,forKey: .privacy)
        let sharing = try container.decode(Access.self,forKey: .sharing)

        self.privacy = AccessModel(privacy)
        self.sharing = AccessModel(sharing)

        if let ids = privacy.ids {
            let model = SomeFriendsPrivacyModel(context: context)
            model.ids = ids
            model.userList = self
            someFriendsPrivacy = model
        }

        if let ids = sharing.ids {
            let model = SomeFriendsSharingModel(context: context)
            model.ids = ids
            model.userList = self
            someFriendsSharing = model
        }

    }

}

使用方法（例如，不安全）：

        let appDelegate = UIApplication.shared.delegate as! AppDelegate
        let context = appDelegate.persistentContainer.viewContext
        let decoder = JSONDecoder()
        decoder.keyDecodingStrategy = .convertFromSnakeCase
        decoder.userInfo[.context] = context
        try! decoder.decode(UserListModel.self,from: json) // json from 1 question
        try! context.save()

1. 如何从Core Data UserListModel初始化UserList模型？

extension Access {
    init?(_ accessModel: AccessModel) {
        switch accessModel {
        case .friendsOnly:
            self = .friendsOnly
        case .private:
            self = .private
        case .public:
            self = .public
        default:
            return nil
        }
    }
}

enum UserListInitError: Error {
    case error(String)
}

extension UserList {

    init(_ listModel: UserListModel) throws {
        if let privacy = Access(listModel.privacy) {
            self.privacy = privacy
        } else {
            guard let ids = listModel.someFriendsPrivacy?.ids else { throw UserListInitError.error("Unable to get data from Core Data model") }
            self.privacy = .someFriends(ids: ids)
        }

        if let sharing = Access(listModel.sharing) {
            self.sharing = sharing
        } else {
            guard let ids = listModel.someFriendsSharing?.ids else { throw UserListInitError.error("Unable to get data from Core Data model") }
            self.sharing = .someFriends(ids: ids)
        }
    }
}

用法（例如，不安全）：

        let appDelegate = UIApplication.shared.delegate as! AppDelegate
        let context = appDelegate.persistentContainer.viewContext
        let request: NSFetchRequest<UserListModel> = UserListModel.fetchRequest()
        let listModel = try! context.fetch(request).first!
        let userList = try! UserList(listModel)