title: No NSEntityDescriptions in any model claim the NSManagedObject subclass
body: <p>I am new to CoreData and I'm trying to create a caching mechanism wherein after parsing objects from the API, I save them to the data model then fetch it again to show it on the tableview. I'm trying to fetch it using <code>NSFetchedResultsController</code>. Upon initialization of the <code>NSFetchedResultsController</code>, I'm encountering this runtime exception:</p>
  
  <pre><code>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 to find a unique match for an 
  NSEntityDescription to a managed object subclass
  </code></pre>
  
  <p>What could be the reason why?</p>