我创建了一个表:键,值。
它只是为了保存一些参数,当键不存在时,我会插入,但当它存在时,我会更新值。
在我的例子中,当键已经存在时,它会在 ma 表中执行另一个插入,键等于 nil:
public static func insertValueWithKey(context: NSManagedObjectContext, key:String, value:String){
let fetchRequest : NSFetchRequest<NSFetchRequestResult>
if #available(iOS 10.0, *) {
fetchRequest = Params.fetchRequest()
} else {
fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Params")
}
let predicate = NSPredicate(format: "key=%@", key)
fetchRequest.predicate = predicate
do {
let results = try context.fetch(fetchRequest)
if(results.count != 0){
let paramsDescription = NSEntityDescription.entity(forEntityName: "Params", in: context)
let params = NSManagedObject(entity: paramsDescription!, insertInto: context) as! Params
params.value = value
do {
try context.save()
} catch let error as NSError {
print ("Error first demande insertion \(error)")
}
} else if (results.count == 0) {
let params = NSEntityDescription.insertNewObject(forEntityName: "Params", into: context) as! Params
params.key = key
params.value = value
context.insert(params)
do {
try context.save()
} catch let error as NSError {
print ("Error first demande insertion \(error)")
}
}
} catch {
let fetchError = error as NSError
print(fetchError)
}
}
我不明白为什么,因为它在模拟器上也能正常工作,但在设备上却不行...
最佳答案
替换:
let params = NSManagedObject(entity: paramsDescription!, insertInto: context) as! Params
与
let params = results.last as! Params
NSManagedObject(entity: insertInto:)
在功能上与 NSEntityDescription.insertNewObject(forEntityName:into:)
关于swift - 核心数据在存在时更新现有对象,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/41570321/