Core Data does not raise an error for an NSManagedObject instance as an application delegate property

Question

I import the registered user data from the server into the main data object called "User". I also keep a reference to this specific User object to my AppDelegate (as a property), so I can access it elsewhere in my application. The problem I am facing is that when I click on another view controller and try to access appdelegate.loggedInUser.id, I see that "id" is zero. The debugger shows this for the object:

$24 = 0x0b28ad30 <User: 0xb28ad30> (entity: User; id: 0xb261160 <x-coredata:///User/tC48E8991-B8A6-4E68-9112-93F9F21DB5382> ; data: <fault>) 

I realized that the Core Data infrastructure will fail with the moment when I try to access one of the properties of this object. I am confused, why am I accessing the user id property, does not raise an error in this case?

EDIT

Here's how to create and use a loggedInUser object:

 //method to get bgContext +(NSManagedObjectContext *)getContextOnBgWithParentSetToMainMOC { NSManagedObjectContext *tmpContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType]; [tmpContext setParentContext:[Utils getAppDelegate].managedObjectContext]; return tmpContext; } //in App Delegate NSManagedObjectContext *bgContext = [NSManagedObjectContext getContextOnBgWithParentSetToMainMOC]; self.loggedInUser = [User importFromObject:loggedInUserData inContext:bgContext completionBlock:^(NSManagedObjectContext *theContext, NSManagedObject *theManagedObjectWithValuesImported) {}]; //In User.m file + (User *)importFromObject:(NSDictionary *)dictionary inContext:(NSManagedObjectContext *)context completionBlock:(TemporaryContextImportReturnBlock)block { if ( !context ){ context = [NSManagedObjectContext getContextOnBgWithParentSetToMainMOC]; } NSManagedObjectContext *localContext = context; User *newUserEntity = [NSEntityDescription insertNewObjectForEntityForName:@"User" inManagedObjectContext:localContext]; NSArray *emailsArray = [dictionary objectForKey:@"emails"]; NSString *emailsString = @""; if ([emailsArray count] > 0){ emailsString = [emailsArray componentsJoinedByString:@","]; } newUserEntity.emails = emailsString; newUserEntity.id = [dictionary objectForKey:@"id"]; newUserEntity.n = [dictionary nonNullObjectForKey:@"n"]; return newUserEntity; } //Access in one of the view controllers User *loggedInUser = [Utils getAppDelegate].loggedInUser; // loggedInUser.id /*nil*/ 

Answer 1

I have the same problem. It turns out, according to this answer , which refers to Apple docs , that a NSManagedObject does not contain a reference to NSManagedObjectContext , as you might expect. I suspect that if you check your object when it does not work correctly, [myObject managedObjectContext] == nil .

I do not know what are the best practices here. The obvious (but potentially difficult) solution is figuring out why your MOC is being freed. Alternatively, although I'm not sure if this is safe, you can save the MOC from each instance of NSManagedObject . (I have a question about this discovery here .)

Answer 2

make sure you don't call

 [managedObjectContext reset]; 

somewhere. From an Apple doc:

Returns the receiver to its base state. All objects controlled by the receiver are “forgotten”. If you use this method, you must make sure that you also drop references to any managed objects retrieved using the receiver, because after that they will be invalid.

These properties of the managedObjectContext managed object change to zero and they will no longer be able to trigger errors.

Answer 3

There is no "save" in your code, before you return newUserEntity, you must call save in your localContext:

 + (User *)importFromObject:(NSDictionary *)dictionary inContext:(NSManagedObjectContext *)context completionBlock:(TemporaryContextImportReturnBlock)block { if ( !context ){ context = [NSManagedObjectContext getContextOnBgWithParentSetToMainMOC]; } NSManagedObjectContext *localContext = context; User *newUserEntity = [NSEntityDescription insertNewObjectForEntityForName:@"User" inManagedObjectContext:localContext]; NSArray *emailsArray = [dictionary objectForKey:@"emails"]; NSString *emailsString = @""; if ([emailsArray count] > 0){ emailsString = [emailsArray componentsJoinedByString:@","]; } newUserEntity.emails = emailsString; newUserEntity.id = [dictionary objectForKey:@"id"]; newUserEntity.n = [dictionary nonNullObjectForKey:@"n"]; NSError *error = nil; [localContext save:&error]; if(error) { NSLog(@"error %@", error); } return newUserEntity; } 

Hope this helps.