iOS – 数据一旦存入Core Data

2019年7月27日 173次阅读

我正在尝试将大量数据保存到核心数据中.我可以设法将所有数据保存到核心数据中,但在核心数据中包含重复数据是没有意义的,因为该函数将在每个项目构建时执行一次.在我添加新记录之前,我现在想的方法是清空实体的记录.只是想知道是否有另一种方法来确保数据只持续一次？

func persistCurrencyData() {
    let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate

    let managedContext = appDelegate.managedObjectContext

    let currencyEntity = NSEntityDescription.entityForName("Currency", inManagedObjectContext: managedContext)


    let countryEntity = NSEntityDescription.entityForName("Country", inManagedObjectContext: managedContext)

    for currency in currencies {
      let currencyObject = CurrencyCore(entity: currencyEntity!, insertIntoManagedObjectContext: managedContext)

      currencyObject.setValue(currency.code, forKeyPath: "code")
      currencyObject.setValue(currency.name, forKeyPath: "name")

      for country in currency.country! {
        let countryObject = CountryCore(entity: countryEntity!, insertIntoManagedObjectContext: managedContext)

        countryObject.setValue(country.name, forKeyPath: "name")
        countryObject.setValue(country.code, forKeyPath: "code")
        countryObject.setValue(country.continent, forKeyPath: "continent")
        countryObject.setValue(country.continentCode, forKeyPath: "continentCode")

        countryObject.currency = currencyObject
      }
    }

    do {
      try managedContext.save()
    } catch let error as NSError  {
      print("Could not save \(error), \(error.userInfo)")
    }
}

更新：

感谢@Wain给我的想法.基本上我所做的是解决在核心数据中保存重复数据的问题,我在JSON文件中包含了一个GUID.每次代码读取JSON文件时,它都会将GUID保存到NSUserDefault中并将数据保存到核心数据中.当它想在下一次构建中再次读取JSON文件时,它将检查GUID是否与先前保存的GUID相同.如果不同,代码将读取JSON文件并重复上述过程.如果没有,它将继续并忽略它.

func requestCurrenciesData() {
    getCurrenciesDataFromFileWithSuccess { (data) -> Void in
      var json: [String: AnyObject]

      do {
        json = try NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions()) as! [String: AnyObject]

        guard let currencyData = CurrencyData(json: json) else {
          print("Error initializing object")
          return
        }

        self.currencies = currencyData.currency!

        // Checking the JSON's id is same as previous read
        let defaults = NSUserDefaults.standardUserDefaults()
        if let id = defaults.stringForKey("id")
        {
          if id == currencyData.id {
            let notification = NSNotification(name: "CurrenciesDataUpdate", object: nil)
            NSNotificationCenter.defaultCenter().postNotification(notification)

            return
          }
        }

        self.persistCurrencyDataForId(currencyData.id)

        let notification = NSNotification(name: "CurrenciesDataUpdate", object: nil)
        NSNotificationCenter.defaultCenter().postNotification(notification)
      } catch {
        print(error)
        return
      }
   }
}

func persistCurrencyDataForId(id: String) {
    // Save the new JSON's id into NSUserDefaults
    let defaults = NSUserDefaults.standardUserDefaults()
    defaults.setObject(id, forKey: "id")

    // Delete all the records in existing table
    deleteRecordsFromEntity("Country")
    deleteRecordsFromEntity("Currency")

    // Insert the new records
    let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let managedContext = appDelegate.managedObjectContext

    let currencyEntity = NSEntityDescription.entityForName("Currency", inManagedObjectContext: managedContext)
    let countryEntity = NSEntityDescription.entityForName("Country", inManagedObjectContext: managedContext)

    for currency in currencies {
      let currencyObject = CurrencyCore(entity: currencyEntity!, insertIntoManagedObjectContext: managedContext)

      currencyObject.setValue(currency.code, forKeyPath: "code")
      currencyObject.setValue(currency.name, forKeyPath: "name")

      for country in currency.country! {
        let countryObject = CountryCore(entity: countryEntity!, insertIntoManagedObjectContext: managedContext)

        countryObject.setValue(country.name, forKeyPath: "name")
        countryObject.setValue(country.code, forKeyPath: "code")
        countryObject.setValue(country.continent, forKeyPath: "continent")
        countryObject.setValue(country.continentCode, forKeyPath: "continentCode")

        countryObject.currency = currencyObject
      }
    }

    do {
      try managedContext.save()
    } catch let error as NSError  {
      print("Could not save \(error), \(error.userInfo)")
    }
  }

func deleteRecordsFromEntity(entityName: String) {
    let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let managedContext = appDelegate.managedObjectContext
    let coordinator = appDelegate.persistentStoreCoordinator

    let fetchRequest = NSFetchRequest(entityName: entityName)
    let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)

    do {
      try coordinator.executeRequest(deleteRequest, withContext: managedContext)
    } catch let error as NSError {
      print(error)
    }
 }

最佳答案 一般来说,你可以说’如果我在数据存储中有任何货币条目,不要添加更多’.这可以通过在第一次导入时添加一个标志来使用默认值或类似的东西来完成,但更好的选择是检查数据存储以查看它是否有任何货币条目.为此,请为currencyEntity创建一个获取请求并使用countForFetchRequest：error：在继续使用货币{.如果计数大于零,那么您应该返回而不是处理循环.

为了提高效率,这个检查实际上应该是在你下载和处理JSON之前…

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