xcode 如何更新核心数据中的现有对象？[迅速]

How to update existing object in core data ? [Swift]

提问by sunny k

I have preloaded data from a .csv file into coredata. I am fetching the data in the following way

我已将 .csv 文件中的数据预加载到 coredata 中。我正在通过以下方式获取数据

var places:[Places] = []

in viewDidLoad:

在viewDidLoad：

if let managedObjectContext = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext {
            let fetchRequest = NSFetchRequest(entityName: "Places")
            do{
                places = try managedObjectContext.executeFetchRequest(fetchRequest) as! [Places]
            }

            catch let error as NSError{
                print("Failed to retrieve record: \(error.localizedDescription)")
            }
        }

In the data there is an attribute isFavorite of type String whose initial value is false. I am changing the value of isFavorite on button click. I want to save the changes made by the user. How can i make this change persistent ?

在数据中有一个字符串类型的属性 isFavorite，其初始值为 false。我正在更改按钮单击时 isFavorite 的值。我想保存用户所做的更改。我怎样才能使这种改变持久化？

Here is my button action

这是我的按钮操作

@IBAction func addToFavourites(sender: AnyObject) {

        cell = tableView.cellForRowAtIndexPath(NSIndexPath(forRow: sender.tag, inSection: 0)) as! CustomTableViewCell
        if cell.isFavouriteLabel.text! == "false" {
            cell.isFavouriteLabel.text = "true"

        }else if cell.isFavouriteLabel.text == "true"{
            cell.isFavouriteLabel.text = "false"

        }
}

Basically i want to set the value of places.isFavourite = cell.isFavoriteLabel.textand save to core data

基本上我想设置值places.isFavourite = cell.isFavoriteLabel.text并保存到核心数据

EDIT: if i try this inside my button action method

编辑：如果我在我的按钮操作方法中尝试这个

if let managedObjectContext = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext {

            let place : Places = Places()
            place.isFavourite = cell.isFavouriteLabel.text
             do{
                try managedObjectContext.save()
            } catch let error as NSError{
                print(error)

            }
          }

i am getting an error: Failed to call designated initializer on NSManagedObject class

我收到一个错误：无法在 NSManagedObject 类上调用指定的初始值设定项

if i simply add this code in the button action method

如果我只是在按钮操作方法中添加此代码

places.isFavourite = cell.isFavouriteLabel.text

i get this error: [Places] does not have a member named isFavourite

我收到此错误：[Places] 没有名为 isFavourite 的成员

采纳答案by MirekE

Your current code is:

您当前的代码是：

if let managedObjectContext = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext {

            let place : Places = Places()
            place.isFavourite = cell.isFavouriteLabel.text
             do{
                try managedObjectContext.save()
            } catch let error as NSError{
                print(error)

            }
          }

That would create a new place (if it worked), but you need to update an existing one.

这将创建一个新位置（如果它有效），但您需要更新现有位置。

You have the placesreturned from managedObjectContext.executeFetchRequest.

您已从places返回managedObjectContext.executeFetchRequest。

So you need to get something like places[index_of_the_cell_in_question].isFavourite = cell.isFavouriteLabel.text

所以你需要得到类似的东西 places[index_of_the_cell_in_question].isFavourite = cell.isFavouriteLabel.text

and then managedObjectContext.save().

然后managedObjectContext.save()。

回答by Bart Hopster

Use the savefunction of the NSManagedObjectContext:

使用saveNSManagedObjectContext的功能：

places.isFavourite = cell.isFavoriteLabel.text

var error: NSError?
if managedObjectContext.save(&error) != true {
    // Error
}

回答by Jér?me Demyttenaere

This is simple as this:

这很简单：

• Find the entry you want to modify in placesthen save the core data context.

  func saveContext () {
      if let moc = self.managedObjectContext {
          var error: NSError? = nil
          if moc.hasChanges && !moc.save(&error) {
              // Replace this implementation with code to handle the error appropriately.
              // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
              println("Unresolved error \(error), \(error!.userInfo)")
              abort()
          }
      }
  }
  

• 找到要修改的条目，places然后保存核心数据上下文。

  func saveContext () {
      if let moc = self.managedObjectContext {
          var error: NSError? = nil
          if moc.hasChanges && !moc.save(&error) {
              // Replace this implementation with code to handle the error appropriately.
              // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
              println("Unresolved error \(error), \(error!.userInfo)")
              abort()
          }
      }
  }
  

I suggest you used a manager to insert, fetch and delete entry in your core data.

我建议您使用管理器在核心数据中插入、获取和删除条目。

import Foundation
import CoreData

class CoreDataHelper: NSObject {

    class var shareInstance:CoreDataHelper {
        struct Static {
            static let instance:CoreDataHelper = CoreDataHelper()
        }
        return Static.instance
    }

    //MARK: - Insert -
    func insertEntityForName(entityName:String) -> AnyObject {
        return NSEntityDescription.insertNewObjectForEntityForName(entityName, inManagedObjectContext: self.managedObjectContext!)
    }

    //MARK: - Fetch -
    func fetchEntitiesForName(entityName:String) -> NSArray {
        ...
    }

    //MARK: - Delete -
    func deleteObject(object:NSManagedObject) {
        self.managedObjectContext!.deleteObject(object)
    }

    // MARK: - Core Data Saving support -
    func saveContext () {
        if let moc = self.managedObjectContext {
            var error: NSError? = nil
            if moc.hasChanges && !moc.save(&error) {
                // Replace this implementation with code to handle the error appropriately.
                // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                println("Unresolved error \(error), \(error!.userInfo)")
                abort()
            }
        }
    }

Hop this can help you

跳这可以帮助你