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。我以下列方式获取数据

  var places：[Places] = [] 
  ：
 pre>  if let managedObjectContext =（UIApplication.sharedApplication（）。delegate as！AppDelegate）.managedObjectContext {
 let fetchRequest = NSFetchRequest（entityName：Places）
 do {
 places = try managedObjectContext.executeFetchRequest（fetchRequest）as！ [Places] 
} 
 
 catch让错误为NSError {
 print（无法检索记录：\（error.localizedDescription））
} 
} 
  

在数据中有一个类型为String的属性isFavorite，其初始值为false。我改变了isFavorite的值在按钮点击。我想保存用户所做的更改。 如何使此更改持续？

以下是我的按钮操作

  @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
 
} 
} 
  

设置 places.isFavourite = cell.isFavoriteLabel.text 的值并保存到核心数据

EDIT ：如果我尝试这里面我的按钮动作方法

 如果let managedObjectContext =（UIApplication.sharedApplication delegate as！AppDelegate）.managedObjectContext {
 
 let place：Places = Places（）
 place.isFavourite = cell.isFavouriteLabel.text 
 do {
 try managedObjectContext。 save（）
} catch let错误为NSError {
 print（error）
 
} 
} 
  

我遇到错误：无法调用NSManagedObject类指定的初始化程序

如果我只是在按钮操作方法中添加此代码

  places.isFavourite = cell.isFavouriteLabel.text 
  
 
 
 
我收到此错误：[Places]没有名为isFavourite的成员
解决方案
您当前的代码是：
 如果让managedObjectContext =（UIApplication.sharedApplication（）。delegate as！ AppDelegate）.managedObjectContext {
 
 let place：Places = Places（）
 place.isFavourite = cell.isFavouriteLabel.text 
 do {
 try managedObjectContext.save 
} catch让错误为NSError {
 print（error）
 
} 
} 
  
这将创建一个新地点（如果有效），但您需要更新现有地点。
 
 
 
从 managedObjectContext.executeFetchRequest 返回 places 。 
 
 
 
所以你需要得到像 places [index_of_the_cell_in_question] .isFavourite = cell.isFavouriteLabel.text  
 
 
 
然后 managedObjectContext.save（）。
 
I have preloaded data from a .csv file into coredata. I am fetching the data in the following way 
var places:[Places] = []
in 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 ?

Here is my button action 
@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.text and save to core data

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)

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

if i simply add this code in the button action method 
places.isFavourite = cell.isFavouriteLabel.text
i get this error : [Places] does not have a member named isFavourite
解决方案
Your current code is:
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.

You have the places returned from managedObjectContext.executeFetchRequest. 

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

and then managedObjectContext.save().

                        
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