如何解决CoreData - 存储一组可转换对象 更新
我有一个具有可转换属性的实体。它是一个自定义对象数组,Reminder
确认为 NSSecureCoding
。
@objc(Reminder)
public class Reminder: NSObject,NSSecureCoding {
public static var supportsSecureCoding: Bool = true
public var date: Date
public var isOn: Bool
public init(date: Date,isOn: Bool) {
self.date = date
self.isOn = isOn
}
struct Keys {
static var date: String = "date"
static let isOn: String = "isOn"
}
public func encode(with aCoder: NSCoder) {
aCoder.encode(date as NSDate,forKey: Keys.date)
aCoder.encode(isOn,forKey: Keys.isOn)
}
required public init?(coder aDecoder: NSCoder) {
guard let date = aDecoder.decodeObject(of: NSDate.self,forKey: Keys.date) as Date? else {
return nil
}
self.date = date
self.isOn = aDecoder.decodeBool(forKey: Keys.isOn)
}
}
下面的代码是我的NSSecureUnarchiveFromDataTransformer
。
class ReminderDataTransformer: NSSecureUnarchiveFromDataTransformer {
override class func allowsReverseTransformation() -> Bool {
return true
}
override class func transformedValueClass() -> AnyClass {
return Reminder.self
}
override class var allowedTopLevelClasses: [AnyClass] {
return [Reminder.self]
}
override func transformedValue(_ value: Any?) -> Any? {
guard let data = value as? Data else {
fatalError("Wrong data type: value must be a Data object; received \(type(of: value))")
}
return super.transformedValue(data)
}
override func reverseTransformedValue(_ value: Any?) -> Any? {
guard let reminder = value as? [Reminder] else {
fatalError("Wrong data type: value must be a Reminder object; received \(type(of: value))")
}
return super.reverseTransformedValue(reminder)
}
}
extension NSValueTransformerName {
static let reminderToDataTransformer = NSValueTransformerName(rawValue: "ReminderToDataTransformer")
}
在初始化 ReminderDataTransformer
之前,我已使用以下代码注册了 NSPersistantContainer
。
ValueTransformer.setValueTransformer(ReminderDataTransformer(),forName: .reminderToDataTransformer)
我在 xCode 的数据模型检查器中使用 ReminderToDataTransformer
作为转换器。
但是因为保存实体时出现以下错误,所以不起作用。
[error] error: sqlCore dispatchRequest: exception handling request: <NSsqlSaveChangesRequestContext: 0x282ec0780>,<shared NSSecureUnarchiveFromData transformer> threw while encoding a value. with userInfo of (null)
CoreData: error: sqlCore dispatchRequest: exception handling request: <NSsqlSaveChangesRequestContext: 0x282ec0780>,<shared NSSecureUnarchiveFromData transformer> threw while encoding a value. with userInfo of (null)
2020-12-31 21:44:09.300394+0100 ReminderApp[26406:6247995] [error] error: -executeRequest: encountered exception = <shared NSSecureUnarchiveFromData transformer> threw while encoding a value. with userInfo = (null)
更新
也不例外。第二次启动应用程序时,此错误会记录在控制台中。
[error] fault: exception raised during multi-threaded fetch <shared NSSecureUnarchiveFromData transformer> threw while decoding a value. ({
NSUnderlyingError = "Error Domain=NSCocoaErrorDomain Code=4864 \"value for key 'root' was of unexpected class 'NSArray (0x1fa392238) [/System/Library/Frameworks/CoreFoundation.framework]'. Allowed classes are '{(\n \"Reminder (0x100fb6920) [/private/var/containers/Bundle/Application/306C3F0B-75AA-4A2D-A934-260B2EB63313/ReminderApp]\”\n)}’.\” UserInfo={NSDebugDescription=value for key 'root' was of unexpected class 'NSArray (0x1fa392238) [/System/Library/Frameworks/CoreFoundation.framework]'.
我想我无法正确编码/解码 Reminder 的数组,因为如果我将代码更改为存储 Reminder
而不是 [Reminder]
,它会起作用。
为了清楚起见,我可以存储 Reminder
,但不能存储 [Reminder]
。
如何将 [Reminder]
存储为 Transformable
?
解决方法
如果您要取消归档数组,则必须将 NSArray
添加到顶级类,这就是我对错误消息的理解
override class var allowedTopLevelClasses: [AnyClass] {
return [NSArray.self,Reminder.self]
}
顺便说一下,考虑将数组编码为 JSON 并将其保存为简单的字符串,而不是可转换的。可以通过计算属性执行转换。
类可以是一个代码量少得多的结构
public struct Reminder : Codable {
public var date: Date
public var isOn: Bool
}
在 NSManagedObject
子类中创建一个 String
属性
@NSManaged public var cdReminders : String
和一个计算属性
var reminders : [Reminder] {
get {
return (try? JSONDecoder().decode([Reminder].self,from: Data(cdReminders.utf8))) ?? []
}
set {
do {
let reminderData = try JSONEncoder().encode(newValue)
cdReminders = String(data: reminderData,encoding:.utf8)!
} catch { cdReminders = "" }
}
}
,
添加到@vadian 的答案中,如果您想包含父数据转换器中允许的顶级类,请尝试
override static var allowedTopLevelClasses: [AnyClass] {
var allowed = super.allowedTopLevelClasses
allowed(contentsOf: [Reminder.self])
return allowed
}
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