swift - 更新 Core Data 中的值会导致 Swift 中出现重复条目

Question

我正在尝试更新 iPad 应用程序的核心数据值。不幸的是，每次我更新数据时，它都会创建一个重复的条目。

我编写了下面的代码，该代码采用包含值的参数并尝试更新。但不幸的是，它创建了一个重复的条目，而不是更新现有的条目。

        let appDelegate = UIApplication.shared.delegate as! AppDelegate

        let context = appDelegate.persistentContainer.viewContext

        let entity = NSEntityDescription.entity(forEntityName: "Project", in: context)
        let newProject = NSManagedObject(entity: entity!, insertInto: context)

        let projectID = 1

        newProject.setValue(projectID, forKey: "projectID")
        newProject.setValue(projectName, forKey: "projectName")
        newProject.setValue(projectFinalDueDate, forKey: "projectFinalDueDate")
        newProject.setValue(ProjectNotes, forKey: "projectNotes")
        newProject.setValue(projectPriority, forKey: "projectPriority")
        newProject.setValue(projectAddedDate, forKey: "projectAddedDate")

        do {
            try context.save()
            showMessage(message: "Successfully update project", messageType: "success")
        } catch {
            showMessage(message: "Failed to update project", messageType: "error")
        }

如果我使用的关键字有误，我很抱歉，请注意，我是 Core Data 的新手，我几天前就开始使用它了。

如果有人能帮我解决这个问题，谢谢

Please find the screen recording of the issue

Answer 1

您在此处创建一个新对象

let newProject = NSManagedObject(entity: entity!, insertInto: context)

因此它将添加一个新对象，您需要使用谓词并根据某个主键更新检索到的值，然后保存上下文，例如

    //As we know that container is set up in the AppDelegates so we need to refer that container.
    guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }
    
    //We need to create a context from this container
    let managedContext = appDelegate.persistentContainer.viewContext
    
    let fetchRequest:NSFetchRequest<NSFetchRequestResult> = NSFetchRequest.init(entityName: "Project")
    fetchRequest.predicate = NSPredicate(format: "projectID  = %d",1)
    do
    {
        let test = try managedContext.fetch(fetchRequest)

         guard let newProject = test.first else { return }
            // update here 
           
           try managedContext.save()                
        }
    catch
    {
        print(error)
    }   
}