[英]CoreData - Store an array of Tranformable objects
I have an entity that has a traformable property.我有一个具有可变形属性的实体。 It is an array of custom object,
Reminder
that confirms to NSSecureCoding
.它是一个自定义 object 的数组,
Reminder
NSSecureCoding
确认。
@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)
}
}
And the following code is my NSSecureUnarchiveFromDataTransformer
.以下代码是我的
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")
}
I have registered ReminderDataTransformer
using the following code before initializing NSPersistantContainer
.在初始化
NSPersistantContainer
之前,我已经使用以下代码注册了ReminderDataTransformer
。
ValueTransformer.setValueTransformer(ReminderDataTransformer(), forName: .reminderToDataTransformer)
I have used ReminderToDataTransformer
as Transformer in xCode's Data Model Inspector.我在 xCode 的 Data Model Inspector 中使用了
ReminderToDataTransformer
作为 Transformer。
But it does not work because of the following error that occurs when saving entities.但它不起作用,因为保存实体时出现以下错误。
[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)
There is no exception.也不例外。 When launching the app for the second time, this error is logged in console.
第二次启动应用程序时,控制台会记录此错误。
[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]'.
I guess I am unable to correctly encode / decode Reminder's array as It works if I change the code to store Reminder
instead of [Reminder]
.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]
,它就可以工作。
Just to be clear, I can store Reminder
, but not [Reminder]
.为了清楚起见,我可以存储
Reminder
,但不能存储[Reminder]
。
How to store [Reminder]
as Transformable
?如何将
[Reminder]
存储为可Transformable
的?
If you are going to unarchive an array you have to add NSArray
to the top level classes, this is how I understand the error message如果要取消归档数组,则必须将
NSArray
添加到顶级类,这就是我理解错误消息的方式
override class var allowedTopLevelClasses: [AnyClass] {
return [NSArray.self, Reminder.self]
}
By the way, instead of a transformable consider to encode the array to JSON and save it as a simple String.顺便说一句,而不是可转换的考虑将数组编码为 JSON 并将其保存为简单的字符串。 The conversion can be performed by a computed property.
转换可以由计算属性执行。
The class can be a struct with dramatically less code class 可以是一个代码少得多的结构
public struct Reminder : Codable {
public var date: Date
public var isOn: Bool
}
In the NSManagedObject
subclass create a String
Attribute在
NSManagedObject
子类中创建一个String
属性
@NSManaged public var cdReminders : String
and a computed property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 = "" }
}
}
Adding to @vadian's answer, if you want to include the allowed top level classes from the parent data transformer, try添加到@vadian 的答案,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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