Codable NSManagedObject 在 decodeIfPresent 数据类型上失败

Question

我在尝试解码时收到此错误 json:

[{
    "id": "76f22c25-cee7-4c7a-94fa-1fb85720f580",
    "purchaseDate": "2012-04-05T19:03:43Z",
    "title": "azare",

}, {
    "id": "9b4b9f7d-382f-4555-9eaa-97939b13633f",
    "purchaseDate": "2012-04-05T19:02:46Z",
    "title": "Chocolat",

}, {
    "id": "02a0aa06-2d0c-4ab9-aaaa-af7dee7b4845",
    "purchaseDate": "2012-09-24T17:39:52Z",
    "title": "Some thing",
}]

Fatal error: 'try!' expression unexpectedly raised an error: Swift.DecodingError.typeMismatch(Swift.Double, Swift.DecodingError.Context(codingPath: [Foundation.(_JSONKey in _12768CA107A31EF2DCE034FD75B541C9)(stringValue: "Index 0", intValue: Optional(0)), MyApp.Purchase.CodingKeys.purchaseDate], debugDescription: "Expected to decode Double but found a string/data instead.", underlyingError: nil)): file /BuildRoot/Library/Caches/com.apple.xbs/Sources/swiftlang/swiftlang-900.0.69.2/src/swift/stdlib/public/core/ErrorType.swift, line 181

My code:

//Purchase+CoreDataClass.swift
@objc(Purchase)
public class Purchase: NSManagedObject, Codable {

    enum CodingKeys: String, CodingKey {
        case id
        case title
        case purchaseDate
    }

required convenience public init(from decoder: Decoder) throws {

var context : NSManagedObjectContext = MyAppCoreDataManager.sharedInstance.persistentContainer.viewContext
        guard let entity = NSEntityDescription.entity(forEntityName: "Purchase", in: context!) else { fatalError() }

        self.init(entity: entity, insertInto: context!)
        let container = try decoder.container(keyedBy: CodingKeys.self)

        self.title = try container.decodeIfPresent(String.self, forKey: .title)
        self.id = try container.decodeIfPresent(String.self, forKey: .id)
        self.purchaseDate = try! container.decodeIfPresent(Date.self, forKey: .purchaseDate)

    }

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

//   Purchase+CoreDataProperties.swift

extension Purchase {

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


    @NSManaged public var id: String?
    @NSManaged public var title: String?
    @NSManaged public var purchaseDate: Date?
}

//CALL

   let decoder = JSONDecoder()

                    decoder.dataDecodingStrategy = .base64
                    let purchases = try decoder.decode([Purchase].self, from: value)

If i remove "purchaseDate" everything works correctly

Answer 1

有一个普遍的误解，错误是关于Date而不是Data

错误发生是因为JSON解码器默认不解码ISO8601日期。默认值是 TimeInterval 又名 Double。

这就是错误消息所说的内容：它需要一个 Double 但找到了一个 String

您必须将解码器的 DateDecodingStrategy 设置为 .iso8601

decoder.dateDecodingStrategy = .iso8601

并去掉try!中的感叹号交错

Codable NSManagedObject 在 decodeIfPresent 数据类型上失败

Codable NSManagedObject fail on decodeIfPresent Data type

nsmanagedobject

swift

codable