将应用程序从Realm迁移到CoreData时，我正在尝试解析以下JSON结构：

{
    "username": "972542052677","displayName": "Arik","countryCode": "972","status": "Busy","walletPublicKey": "XgWDiGMFRPDRVnRq8nxu7NyMLuT4Uez7mJ","lastSeen": "2020-08-05T08:12:57.5267881","isOnline": false
}

我需要从该数据创建一个NSManagedObject，因此我在关注本教程： https://medium.com/@andrea.prearo/working-with-codable-and-core-data-83983e77198e

这是模型。它继承自自动生成的“ ManagedProfile”类：

class ManagedProfileCodable: ManagedProfile,Codable {

enum CodingKeys: String,CodingKey {
    case username           = "username"
    case displayName        = "displayName"
    case email              = "email"
    case status             = "status"
    case walletPublicKey    = "walletPublicKey"
    case countryCode        = "countryCode"
    case isOnline           = "isOnline"
    case lastSeen           = "lastSeen"
}

// MARK: - Decodable
required convenience init(from decoder: Decoder) throws {
    guard let codingUserInfoKeymanagedobjectcontext = CodingUserInfoKey.managedobjectcontext else{
        fatalError("Failed to get codingUserInfoKeymanagedobjectcontext")
    }
    
    guard let managedobjectcontext = decoder.userInfo[codingUserInfoKeymanagedobjectcontext] as? NSmanagedobjectcontext else{
        fatalError("Failed to get context from decoder")
    }
    guard let entity = NSEntityDescription.entity(forEntityName: "ManagedProfile",in: managedobjectcontext) else {
        fatalError("Failed to read entity desc")
    }
    
    self.init(entity: entity,insertInto: managedobjectcontext)

    let container =     try decoder.container(keyedBy: CodingKeys.self)

    self.username =     try container.decodeIfPresent(String.self,forKey: .username)
    self.displayName =  try container.decodeIfPresent(String.self,forKey: .displayName)
    self.email =        try container.decodeIfPresent(String.self,forKey: .email)
    self.status =       try container.decodeIfPresent(String.self,forKey: .status)
    self.walletPublicKey =  try container.decodeIfPresent(String.self,forKey: .walletPublicKey)
    self.isOnline =     try container.decodeIfPresent(Bool.self,forKey: .isOnline) ?? false
    self.countryCode = try container.decodeIfPresent(String.self,forKey: .countryCode)
    
}
// MARK: - Encodable
public func encode(to encoder: Encoder) throws {
    
    var container = encoder.container(keyedBy: CodingKeys.self)
    try container.encode(username,forKey: .username)
    try container.encode(username,forKey: .displayName)
    try container.encode(username,forKey: .email)
    try container.encode(username,forKey: .countryCode)
    try container.encode(username,forKey: .lastSeen)
    try container.encode(username,forKey: .walletPublicKey)
    try container.encode(username,forKey: .status)
    try container.encode(username,forKey: .isOnline)
}}

这是解码器：

var jsonDecoder : JSONDecoder = {
        let decoder = JSONDecoder()
        if let appDelegate = UIApplication.shared.delegate as? AppDelegate{
            if let codingUserInfoKeymanagedobjectcontext = CodingUserInfoKey.managedobjectcontext{
                decoder.userInfo[codingUserInfoKeymanagedobjectcontext] = appDelegate.persistentContainer.viewContext
            }
        }
        return decoder
    }()

这是执行实际解码的部分。 T代表ManagedProfileCodable，并且existData变量包含一个有效的json（我使用较旧的JSONSerialization库成功对其进行了编码，以确保其有效）

        do
        {
            let result = try jsonDecoder.decode(T.self,from: existingData)
            DispatchQueue.main.async{
                completionHandler(NetworkResult<T>.success(result))}
        }
        catch let error {
...
        }

这是我收到的错误：

▿valueNotFound：2个元素

• .0：TwoVerte.ManagedProfileCodable

▿.1：上下文

• codingPath：0个元素
• debugDescription：“给定的数据不包含顶级值。”
• underlyingError：无

我遇到了另一位开发人员的未回答帖子，他在此处描述了相同的问题：CoreData NSManagedObject & JSON Encodable not working

由于JSON有效且到达了initFromDecoder内部的断点，所以我想不出任何可能导致此失败的原因。建立类的方式可能出了问题。我想知道是否还有其他人也遇到过类似的问题。