Deleting a record from Core Data

Question

I'm having trouble deleting records from Core Data SQLite file. I want to be able to delete the corresponding record from my file when I delete a row from my table view.

Here is what I am doing after fetching all records into allContacts array

NSManagedObject *contactRecord = [allContacts objectAtIndex:arc4random() % allContacts.count];
self.managedObjectID = [contactRecord objectID];

Then called my method that prepares my contacts and then display them on the tableview.

When I delete a row from the table, I call this method

-(void)deleteContactFromFile:(contact *)deletedContact
{
    NSLog(@"deleted Contact %@",deletedContact.personID);
    AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
    NSManagedObjectContext *context = appDelegate.managedObjectContext;
    [context deleteObject:[context objectWithID:self.managedObjectID]];
    [context save:nil];
}

The funny thing is I get a random record deleted from my core data file, but not the one I selected. I don't know how to deal with ObjectID thing for deleting a specific NSManagedObject.

If my question is not clear enough please tell me to clarify more.

Answer 1

You should be using an NSFetchedResultsController. It will help you to associate every index path of your table view with a specific managed object. You then do not need to fetch all data and filter through them.

For example, if you have the index path and a fetched results controller it is as easy as

NSManagedObject *object = [self.fetchedResultsController objectAtIndexPath:indexPath];
NSManagedObjectContext *context = object.managedObjectContext;
[context deleteObject:object]; 
[context save:nil]; 

Note that you not need to go to your app delegate to get the managed object context.

Answer 2

Try this:

- (void)deleteContactFromFile:(contact *)deletedContact {
    NSManagedObjectContext *context = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
    NSFetchRequest *fetchRequest = [NSFetchRequest new];
    [fetchRequest setEntity:[NSEntityDescription entityForName:@"EntityName" inManagedObjectContext:context]];
    NSError *error;
    NSArray *rootArray = [context executeFetchRequest:fetchRequest error:&error];
    for (NSManagedObject *object in rootArray) {
        if ([context objectWithID:self.managedObjectID]) {
            [context deleteObject:object];
        }
    }
}