我看到的所有相关问题都在Objective C中，但我使用的是Swift . 我在核心数据中有一对多关系，一个“当前”实体与许多“预测”实体有关系 . 我设法保存并获取“当前”实体，但未能为我的表“预测”实体的“匹配”执行此操作 . Forecast实体也应该显示在UITableView中 . 这就是我现在所拥有的 . 我正在尝试创建的数组总是空的 . 我需要一些帮助：
guard let stack = (UIApplication.shared.delegate as! AppDelegate).stack else {return}
let sortDescriptors = [NSSortDescriptor(key: "city_id_forecast", ascending: true)]
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Forecast")
fetchRequest.sortDescriptors = sortDescriptors
fetchRequest.predicate = NSPredicate(format: "main==%@", currentFetched!)
if (currentFetched==nil){
print("current fetched is nil")
}
else{
print("currentFetched is not nil")
}
let fetchedResultController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: stack.context, sectionNameKeyPath: "city_id_forecast", cacheName: nil)
do {try fetchedResultController.performFetch()}
catch {print ("error in performing fetch results\(error)")}
let fetched = fetchedResultController.fetchedObjects
//let fetched = fetchedResultController.
let count = fetched?.count
print ("count of fetched forecast!: \(count!)")
for i in 0..<count!{
let currentFetched = fetched?[i] as? Forecast
let dateForecast = currentFetched?.value(forKeyPath: "date_forecast") as! String
let tempForecast = currentFetched?.value(forKeyPath: "temperature_forecast") as! String
let iconForecast = currentFetched?.value(forKeyPath: "icon_forecast") as! String
let forecastElement = "\(dateForecast), \(tempForecast), \(iconForecast)"
forecastArray.append(forecastElement)