使用 UUID 的 Swift 5 CoreData 谓词 [英] Swift 5 CoreData predicate using UUID

问题描述

我有一个实体，我为其设置了一些 ID 作为 UUID 对象.我有这个功能来检查它是否已经记录在持久存储中.

I have an entity for which I set some ID as UUID object. And I have this function to check if it is already recorded in the persistent store.

我发现了一些不起作用的示例，因为示例使用了一些 'NSPredicate(format: "%K == %@", #KeyPath(attribute), id)' 在 swift 中不起作用的代码.

I had found some forme of example that did not work as the example was using some 'NSPredicate(format: "%K == %@", #KeyPath(attribute), id)' code that does not work in swift.

所以我想弄清楚我是如何快速解决这个问题的.我不想将 UUID 存储为一个简单的字符串，因为 coreData 允许我们保存 UUID 对象.

So I am trying to figure out how I go about this in swift. I would prefer not to store the UUID as a simple string since coreData lets us save UUID object.

我有这个方法，但它在 NSPredicate 行上崩溃了:

I have this method but it is crashing on the NSPredicate line:

static func isKnownBikeID(_ bleID: UUID) -> Bool {
    let context = A18DataStore.shared.viewContext
    let fetchRequest = NSFetchRequest<NSManagedObject>(entityName: "Bike")
    fetchRequest.predicate = NSPredicate(format: "%K == %@", [\Bike.bleID , bleID] as CVarArg)
    do{
        let bikes = try context.fetch(fetchRequest)
        return bikes.count > 0
    }
    catch let error as NSError {
        print("Could not fetch. \(error), \(error.userInfo)")
    }
    return false
}

我的当前方法出现异常:

I get en exception with my curent method:

2021-07-16 11:55:28.390629-0400 A18 UAT[9260:4171027] -[Swift.__SwiftDeferredNSArray rangeOfString:]: unrecognized selector sent to instance 0x282c22cc0

推荐答案

• %K 格式需要一个关键路径字符串，这可以使用 #keyPath 指令获得.
• %@ 格式需要一个 Objective-C 对象，这里我们可以使用 UUID 和 NSUUID 之间的免费桥接.
• The %K format expects a key path string, this can be obtained using the #keyPath directive.
• The %@ format expects an Objective-C object, here we can use the toll-free bridging between UUID and NSUUID.

这给出:

let predicate = NSPredicate(format: "%K == %@",
                            #keyPath(Bike.bleID), bleID as NSUUID)

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