Retrieving NSManagedObjects Issue (Core Data) - ios

Question

Here is my issue, I am using core data to store around 58 documents. All they have is 4 NSString attributes. I have a helper class that is set up to retrieve documents whenever I need them, however when I passed back the array from my initial getAllDocumentsFromCoreData, all of the attributes seem to be null when accessed in downloadDocumentPDFsAndStoreOnDeviceViaWebService.
The weird thing is when I go to view the array fetched from core data in the getAllDocumentsFromCoreData method, it shows all of the documents/attributes correctly fetched.
What am I doing wrong? I'm relatively new to Core Data, so this could be a rookie mistake.
//USE TO RETRIEVE ALL DOCUMENTS CURRENTLY STORED WITHIN COREDATA
+ (NSArray *) getAllDocumentsFromCoreData
{
CoreData_Helper *helper = [[CoreData_Helper alloc] init];
NSManagedObjectContext *context = [helper managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setReturnsObjectsAsFaults: NO];
NSEntityDescription *entity = [NSEntityDescription entityForName: #"Document" inManagedObjectContext: context];
[fetchRequest setEntity: entity];
NSError *error = nil;
NSArray *fetchedDocuments = [context executeFetchRequest: fetchRequest error: &error];
if (error)
{
NSLog(#"%#", [error localizedDescription]);
}
return fetchedDocuments;
}
+ (void) downloadDocumentPDFsAndStoreOnDeviceViaWebService
{
NSArray *fetchedDocuments = [CoreData_Helper getAllDocumentsFromCoreData];
for (Document *document in fetchedDocuments)
{
NSLog(#"%#", [document fileID]);
}
}

Answer 1

This is happening because:
Managed objects don't have strong references to their managed object context
When a managed object context is deallocated, any managed objects fetched from it become inaccessible, with attribute values set to nil, because they no longer have any connection to the persistent store.
In your case you're allocating a managed object context in getAllDocumentsFromCoreData and performing your fetch. You return the results but the context gets deallocated at the end of the function. By the time you look at the returned array, the context is gone and the objects are useless.
You should create the managed object context somewhere else-- probably (though not necessarily) as a property of the object where these methods exist. It's typical to have relatively long-lived context objects rather than create them locally just before performing a fetch. There are various other techniques, but the key in your case is that you must not let the context be deallocated until you're finished with everything you've fetched from it.