核心数据在存在时更新现有对象

Question

我创建了一个表：key，value。

这只是为了保存一些参数，当键不存在时，我做一个插入，但是当它存在时，我更新值。

在我的情况下，当键已经存在它在马表的另一插入与关键等于零：

public static func insertValueWithKey(context: NSManagedObjectContext, key:String, value:String){ 

    let fetchRequest : NSFetchRequest<NSFetchRequestResult> 

    if #available(iOS 10.0, *) { 
     fetchRequest = Params.fetchRequest() 
    } else { 
     fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Params") 
    } 

    let predicate = NSPredicate(format: "key=%@", key) 
    fetchRequest.predicate = predicate 

    do { 
     let results = try context.fetch(fetchRequest) 

     if(results.count != 0){ 

      let paramsDescription = NSEntityDescription.entity(forEntityName: "Params", in: context) 


      let params = NSManagedObject(entity: paramsDescription!, insertInto: context) as! Params 


      params.value = value 

      do { 
       try context.save() 
      } catch let error as NSError { 
       print ("Error first demande insertion \(error)") 
      } 

     } else if (results.count == 0) { 

      let params = NSEntityDescription.insertNewObject(forEntityName: "Params", into: context) as! Params 

      params.key = key 
      params.value = value 

      context.insert(params) 

      do { 
       try context.save() 
      } catch let error as NSError { 
       print ("Error first demande insertion \(error)") 
      } 
     } 


    } catch { 
     let fetchError = error as NSError 
     print(fetchError) 
    } 

} 

我不明白为什么，因为它的工作以及在模拟器但不是设备...

Answer 1

取代：

let params = NSManagedObject(entity: paramsDescription!, insertInto: context) as! Params 

与

let params = results.last as! Params 

NSManagedObject(entity: insertInto:)与功能上相同NSEntityDescription.insertNewObject(forEntityName:into:)