ios - 在将实体保存到核心数据 swift4 之前检查实体是否存在。

Question

我正在尝试将数据添加到应用程序中的核心数据中。当我保存它而不检查它是否已经存在时，它工作正常。但我不知道我的核心数据中有什么重复项，所以我所做的就是获取所有具有我尝试添加的实体名称的实体，然后检查它是否为 0，否则我添加它。但我在尝试保存时不断收到错误。如果有人能帮我解决这个问题。

这是我的检查功能:

func entityExists(name: String) -> Bool {
    let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "name")
    fetchRequest.includesSubentities = false

    var entitiesCount = 0

    do {
        entitiesCount = try coreDataController.mainContext.count(for:         fetchRequest)
    }
    catch {
        print("error executing fetch request: \(error)")
    }

    if entitiesCount == 0{
        return true
    } else {
        return false
    }
}

这是我保存数据时的代码。

if entityExists(name: (scrimmagePassedOver?.name)!) == true{

    coreDataController.saveContext()
    NotificationCenter.default.post(name: NSNotification.Name(rawValue: "load"), object: nil)

    let alert = UIAlertController(title: "Saved!", message: "You have saved your Scrimmage.", preferredStyle: UIAlertControllerStyle.alert)

   // add an action (button)
    alert.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.default, handler: nil))
    self.present(alert, animated: true, completion: nil)
   } else {
    let alert = UIAlertController(title: "hey", message: "You have saved this Scrimmage before.", preferredStyle: UIAlertControllerStyle.alert)
   alert.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.default, handler: nil))
   self.present(alert, animated: true, completion: nil)
    }

Answer 1

您可以像这样从核心数据中检查记录:

func checkRecordExists(entity: String,uniqueIdentity: String,idAttributeName:String) -> Bool {
    let context = getManagedObjectContext()
    let fetchRequest = NSFetchRequest<NSManagedObject>(entityName: entity)
    fetchRequest.predicate = NSPredicate(format: "\(idAttributeName) CONTAINS[cd] %@", createdDate)

    var results: [NSManagedObject] = []

    do {
        results = try context.fetch(fetchRequest)
    }
    catch {
        print("error executing fetch request: \(error)")
    }

    return results.count > 0

}

和managedObjectContext是:

func getManagedObjectContext() -> NSManagedObjectContext{

    let delegate = UIApplication.shared.delegate as? AppDelegate

    return delegate!.persistentContainer.viewContext
} 

如果您得到false，则保存它。