如何更新核心数据中的现有对象?[迅速] [英] How to update existing object in core data ? [Swift]

问题描述

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

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

var places:[Places] = []

在 viewDidLoad 中:

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)")
            }
        }

在数据中有一个字符串类型的属性isFavorite，它的初始值为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.我如何才能使这种更改持久化?

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 ?

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"

        }
}

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

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

编辑:如果我在我的按钮操作方法中尝试这个

EDIT : if i try this inside my button action method

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)

            }
          }

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

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

如果我只是在按钮操作方法中添加此代码

if i simply add this code in the button action method

places.isFavourite = cell.isFavouriteLabel.text

我收到这个错误:[Places] 没有名为 isFavourite 的成员

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

推荐答案

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)

            }
          }

这将创建一个新地点(如果它有效)，但您需要更新现有地点.

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

您拥有从 managedObjectContext.executeFetchRequest 返回的 places.

You have the places returned from managedObjectContext.executeFetchRequest.

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

然后managedObjectContext.save().

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