CoreData - 存儲一組可轉換對象

Question

我有一個具有可變形屬性的實體。 它是一個自定義 object 的數組， Reminder NSSecureCoding確認。

@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)
    }
}

---

以下代碼是我的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NSPersistantContainer之前，我已經使用以下代碼注冊了ReminderDataTransformer 。

ValueTransformer.setValueTransformer(ReminderDataTransformer(), forName: .reminderToDataTransformer)

---

我在 xCode 的 Data Model Inspector 中使用了ReminderToDataTransformer作為 Transformer。

---

但它不起作用，因為保存實體時出現以下錯誤。

 [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。 第二次啟動應用程序時，控制台會記錄此錯誤。

[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]'. 

---

我想我無法正確編碼/解碼 Reminder 的數組，因為如果我將代碼更改為存儲Reminder而不是[Reminder] ，它就可以工作。

為了清楚起見，我可以存儲Reminder ，但不能存儲[Reminder] 。

---

如何將[Reminder]存儲為可Transformable的？

---

Answer 1

如果要取消歸檔數組，則必須將NSArray添加到頂級類，這就是我理解錯誤消息的方式

override class var allowedTopLevelClasses: [AnyClass] {
    return [NSArray.self, Reminder.self]
}

---

順便說一句，而不是可轉換的考慮將數組編碼為 JSON 並將其保存為簡單的字符串。 轉換可以由計算屬性執行。

class 可以是一個代碼少得多的結構

public struct Reminder : Codable {
    public var date: Date
    public var isOn: Bool
}

在NSManagedObject子類中創建一個String屬性

@NSManaged public var cdReminders : String

和一個計算屬性

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 = "" }
    }
}

Answer 2

添加到@vadian 的答案，如果您想包含父數據轉換器中允許的頂級類，請嘗試

override static var allowedTopLevelClasses: [AnyClass] {
    var allowed = super.allowedTopLevelClasses
    allowed(contentsOf: [Reminder.self])
    
    return allowed
}