ios - 更新 CoreData 实体或保存一个新实体

Question

我是 CoreData 的新手，我正在尝试制作游戏。我有几个问题，希望你们能帮我一些指导:
- GameKit 是否已经集成了某种 CoreData？如果 GameKit 中已经有替代它的东西，我不确定我是否对这个 CoreData 东西想得太多了。 . . .
无论如何，假设上述问题的答案是“不。GameKit 没有任何东西可以保存你的游戏”。我将继续使用当前的“保存游戏”代码，如下所示:

func saveCurrentMatch()
    {
        /* CORE DATA STUFF:
         FIRST NEED TO VERIFY IF THIS GAME HAS BEEN PREVIOUSLY SAVED, IF SO THEN UPDATE, ELSE JUST SAVE
         Entity: MatchData
         Attributes: scoreArray (String), playerArray (String), myScore (Int), matchID (Int), isWaiting (Bool), isRealTime (Bool), gameLog (String)
         */

        let context = myAppDelegate.persistentContainer.viewContext
        let request = NSFetchRequest<NSFetchRequestResult>(entityName: "MatchData")
        request.returnsObjectsAsFaults = false

        do
        {
            let gamesInProgress = try context.fetch(request)
            print (gamesInProgress.count)

            if gamesInProgress.count > 0 //HERE CHANGE THIS TO LOOK FOR THE MATCH ID OF THIS GAME!!
            {
                gameExistsinCD = true
            }
            else
            {
                gameExistsinCD = false
            }
        }
        catch
        {
            print ("Error Reading Data: \(error.localizedDescription)")
        }

        if gameExistsinCD
        {
            //CODE TO UPDATE MATCH INSTEAD OF SAVING NEW ONE
        }
        else
        {
            // CODE TO SAVE A NEW MATCH FOR THE FIRST TIME
            let matchData = NSEntityDescription.insertNewObject(forEntityName: "MatchData", into: context)

            matchData.setValue(isRealTime, forKey: "isRealTime")
            matchData.setValue(currentScore?[0], forKey: "myScore")
            matchData.setValue(currentScore?.map{String($0)}.joined(separator: "\t"), forKey: "scoreArray") // IS THIS CODE CORRECT? I'M TRYING TO SAVE AN ARRAY OF INTS INTO A SINGLE STRING
            matchData.setValue(currentPlayers?.joined(separator: "\t"), forKey: "playerArray")
            matchData.setValue(true, forKey: "isWaiting") //will change later to update accordingly.
            matchData.setValue(matchID, forKey: "matchID")
            matchData.setValue(gameLog, forKey: "gameLog")

            do
            {
                try context.save()
                print ("CoreData: Game Saved!")
            }
            catch
            {
                print ("Error Saving Data: \(error.localizedDescription)")
            }
        }
    }

我主要关心的是获取请求，如果这个匹配项已经保存，我该如何检查所有的核心数据？如果是这样，更新实体而不是插入新实体的代码是什么？
感谢任何指导，谢谢!

Answer 1

不要让 Core Data 吓到您。它可以是保存本地数据的好方法，尽管有一些评论，但如果做得好，速度并不慢。事实上，Core Data 可以非常快。

通过以更正常的方式使用 Object 类而不是使用 setValue 调用，您可以大大简化代码。您的创建代码可以更改为:

// CODE TO SAVE A NEW MATCH FOR THE FIRST TIME
if let matchData = NSEntityDescription.insertNewObject(forEntityName: "MatchData", into: context) as? MatchData {

    matchData.isRealTime = isRealTime
    matchData.myScore = currentScore?[0]
    matchData.scoreArray = currentScore?.map{String($0)}.joined(separator: "\t") // IS THIS CODE CORRECT? I'M TRYING TO SAVE AN ARRAY OF INTS INTO A SINGLE STRING
    // You can certainly save it this way and code it in and out. A better alternative is to have a child relationship to another managed object class that has the scores.
    matchData.playerArray = currentPlayers?.joined(separator: "\t")
    matchData.isWaiting = true
    matchData.matchID = matchID
    matchData.gameLog = gameLog
}

这是设置对象属性的一种更具可读性和常规的方式。每次更改核心数据托管对象的属性时，下次保存上下文时都会保存该属性。

就查找与 ID 匹配的当前记录而言，我喜欢将类似的类添加到我的托管对象类本身:

class func findByID(_ matchID: String) -> MatchData? {
    let myAppDelegate = UIApplication.shared.delegate as! AppDelegate
    let context = myAppDelegate.persistentContainer.viewContext
    let request = NSFetchRequest<NSFetchRequestResult>(entityName: "MatchData")
    let idPredicate = NSPredicate(format: "matchID = \(matchID)", argumentArray: nil)
    request.predicate = idPredicate
    var result: [AnyObject]?
    var matchData: MatchData? = nil
    do {
        result = try context.fetch(request)
    } catch let error as NSError {
        NSLog("Error getting match: \(error)")
        result = nil
    }
    if result != nil {
        for resultItem : AnyObject in result! {
            matchData = resultItem as? MatchData
        }
    }
    return matchData
}

然后在任何需要通过 ID 匹配数据的地方都可以调用类函数:

if let matchData = MatchData.findByID("SomeMatchID") {
    // Match exists
}