我是CoreData的新手，我正在尝试创建一种缓存机制，其中从API解析对象之后，将它们保存到数据模型中，然后再次获取它以在tableview上显示它。我正在尝试使用获取它NSFetchedResultsController。在初始化时NSFetchedResultsController，我遇到了以下运行时异常：
2018-12-09 15:03:20.493509+0800 [5184:148001] [error] error:
No NSEntityDescriptions in any model claim the NSManagedObject subclass
'Product' so +entity is confused. Have you loaded your
NSManagedObjectModel yet ?
CoreData: error: No NSEntityDescriptions in any model claim the
NSManagedObject subclass 'Product' so +entity is confused. Have you
loaded your NSManagedObjectModel yet ?
2018-12-09 15:03:20.493718+0800[5184:148001] [error] error: +
[Product entity] Failed to find a unique match for an
NSEntityDescription to a managed object subclass
CoreData: error: +[Product entity] Failed …