Question

我想将数据保存到CoreData，但是我收到了下一个错误：

Terminating app due to uncaught exception 'NSUnknownKeyException',
reason: '[<NSEntityDescription 0x7fc428f75940> setValue:forUndefinedKey:]: 
this class is not key value coding-compliant for the key username.'

这是我的代码：

let appDelegate: AppDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let context: NSManagedObjectContext = appDelegate.managedObjectContext

    let request: NSFetchRequest = NSFetchRequest(entityName: "UnreadMessages")
    request.returnsObjectsAsFaults = false

    do {
        let result: NSArray = try context.executeFetchRequest(request)
        let newRecord: NSEntityDescription = NSEntityDescription.entityForName("UnreadMessages", inManagedObjectContext: context)!

        if result.count > 0 {
            print("It exists")
            print(context)
        } else {
            print("it's a new record")
            newRecord.setValue(user.jidStr, forKey: "username")
            newRecord.setValue("1", forKey: "count")

            do {
                try context.save()
            } catch let error {
                print(error)
            }
            print(context)
        }
    } catch _ {

    }

直到：

print("it's a new record")
newRecord.setValue(user.jidStr, forKey: "username")

打印It's a new record并崩溃！我的代码出了什么问题？

这是我的CoreData截图：

Answer 1

因未捕获的异常终止应用＆＃39; NSUnknownKeyException＆＃39;，原因：＆＃39; [ setValue：forUndefinedKey：]：此类不是键值符合编码的密钥用户名。＆＃39;

这是你的大线索。这意味着您要求NSEntityDescription的实例使用KVC设置名称为＆＃34; username＆＃34;但那个班不支持那个键。

打印出新记录并崩溃！我的代码出了什么问题？

嗯，您的代码不会创建新的＆＃34;记录。＆＃34;这段代码

let newRecord: NSEntityDescription = NSEntityDescription.entityForName("UnreadMessages", inManagedObjectContext: context)!

创建NSEntityDescription，可用于创建NSManagedObject。

创建一个新的＆＃34;记录＆＃34;你想打电话

let newRecord = NSEntityDescription.insertNewObjectForEntityForName(
                    "UnreadMessages",
                    inManagedObjectContext:context)

因此，您现在可以看到您正在设置＆＃34;用户名＆＃34;在实体描述上，而不是托管对象。

Answer 2

我认为如果找不到匹配的记录，首先需要插入托管对象上下文...

   do {
    let result: NSArray = try context.executeFetchRequest(request)
    if result.count > 0 {
        // NEW CODE: Print the username if found in result[0]                         
        let userFound = result[0]                                                 
        let usernamefound = String(userFound.valueForKey("username")!)            
        print("It exists  \(usernameFound)")                                      

        print(context)
    } else {
        print("it's a new record")

        let newRecordEntity: NSEntityDescription = NSEntityDescription.entityForName("UnreadMessages", inManagedObjectContext: context)!
        let newRecord = UnreadMessages(entity: newRecordEntity!, insertIntoManagedObjectContext: context)

        newRecord.setValue(user.jidStr, forKey: "username")
        newRecord.setValue("1", forKey: "count")

        do {
            try context.save()
        } catch let error {
            print(error)
        }

我尝试向Core Data添加新记录时出错

2 个答案: