iOS Swift |核心數據提取由特定值

Question

我有這個模型的核心數據：

class Posts: NSManagedObject { 
@NSManaged var title: String? 
@NSManaged var author: String? 
@NSManaged var url: String? 
@NSManaged var isFavorite: NSNumber? 
} 

我要收藏夾功能添加到我的應用程序。

如何獲取具有屬性isFavorite == true的實體？到目前爲止，我已經設法獲取所有數據，但我需要具有特定isFavorite值的數據。

Answer 1

只抓取具有favorite = true的對象很容易，你只需要用它設置一個謂詞。像這樣的東西應該會給你一些指示燈：

class func fetchFavourites(managedObjectContext: NSManagedObjectContext)->[Posts]{ 

    let fetchRequest = NSFetchRequest(entityName: "Posts") 
    let predicate = NSPredicate(format: "isFavorite = \(NSNumber(bool:true))") 

    fetchRequest.predicate = predicate 

    do { 

     let results = try managedObjectContext.executeFetchRequest(fetchRequest) as! [Posts] 
     return results 

    } catch let error as NSError { 

    } 

    return [] 
}