How to reset CoreData Application

Question

I am trying, to reset my app which uses Core Data, for this, I have written the code below

- (void) resetApplicationModel
{
//    NSError *error;
    NSError *error;
    // retrieve the store URL
    NSURL * storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"abc.sqlite"];
    // lock the current context
    [self.managedObjectContext lock];

   [self.managedObjectContext reset];//to drop pending changes
    //delete the store from the current managedObjectContext
    if ([[self.managedObjectContext persistentStoreCoordinator] removePersistentStore:[[[self.managedObjectContext persistentStoreCoordinator] persistentStores] lastObject] error:&error])
    {
        // remove the file containing the data
        if([[NSFileManager defaultManager] removeItemAtURL:storeURL error:&error])
        {
            //recreate the store like in the appDelegate method
            if([[self.managedObjectContext persistentStoreCoordinator] addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error] == nil)
            {
                NSLog( @"could not create new persistent store at %@ - %@", [storeURL absoluteString], [error localizedDescription]);
            }
        }
        else
        {
            NSLog( @"could not remove the store URL at %@ - %@", [storeURL absoluteString], [error localizedDescription]);
        }

    }
    else
    {
        NSLog( @"could not remove persistent store - %@", [error localizedDescription]);
    }
    [self.managedObjectContext unlock];

      __managedObjectContext = nil;

    [self managedObjectContext];

    _rootViewController.controller = nil;//Make NSFetchResultsController nil;

}

This code works fine on ios 6.1 simulator and there are no issues, but when I check this on iphone 4 running iOS 6.1.3, the persistence file is not deleted and I get error saying

"could not remove the store URL at file://localhost/var/mobile/Applications/147E198E-FAB9-46EA-BE4B-4411AFA013FB/Documents/abc.sqlite - The operation couldn’t be completed. (Cocoa error 4.)"

But all the data is deleted, Now when I try to add new Data inside coreData , I get a error saying

" Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'This NSPersistentStoreCoordinator has no persistent stores. It cannot perform a save operation.'"

Please help me guys

Regards Ranjit

Answer 1

Create a category on NSManagedObjectContext then implement:

- (BOOL)deleteAllObjectsForEntityName:(NSString *)entity withError:(NSError *__autoreleasing *)error {

NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:[NSEntityDescription entityForName:entity inManagedObjectContext:self]];
[request setIncludesPropertyValues:NO];

NSArray *allObjects = [self executeFetchRequest:request error:error];

if (![self save:error])
    return NO;

for (NSManagedObject *object in allObjects)
    [self deleteObject:object];

return YES;
}

Then to use this simply do:

- (void)deleteAllObjectsForEntityName:(NSString *) entity {

   NSError *error = nil;
   NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
   if (managedObjectContext != nil) {
       if (![managedObjectContext deleteAllObjectsForEntityName:entity withError:&error]) {
           NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    }
 }
}

Pass your entity name in and it will delete it all :-)