EXC_MEMORY_ACCESS when trying to delete from Core Data ($cash solution)

Question

I have an application that downloads an xml file, parses the file, and creates core data objects while doing so. In the parse code I have a function called 'emptydatacontext' that removes all items from Core Data before creating replacements items from the xml data. This method looks like this:

-(void) emptyDataContext
{
NSFetchRequest * allCon = [[NSFetchRequest alloc] init];
[allCon setEntity:[NSEntityDescription entityForName:@"Condition" inManagedObjectContext:managedObjectContext]];
NSError * error = nil;
NSArray * conditions = [managedObjectContext executeFetchRequest:allCon error:&error];
DebugLog(@"ERROR: %@",error);
DebugLog(@"RETRIEVED: %@", conditions);
[allCon release];

for (NSManagedObject * condition in conditions) {
    [managedObjectContext deleteObject:condition];
}

// Update the data model effectivly removing the objects we removed above.
//NSError *error;
if (![managedObjectContext save:&error]) {
    DebugLog(@"%@", [error domain]);
}

}

The first time this runs it deletes all objects and functions as it should - creating new objects from the xml file. I created a 'update' button that starts the exact same process of retrieving the file the proceeding with the parse & build. All is well until its time to delete the core data objects. This 'deleteObject' call creates a "EXC_BAD_ACCESS" error each time. This only happens on the second time through.

Captured errors return null. If I log the 'conditions' array I get a list of NSManagedObjects on the first run. On the second this log request causes a crash exactly as the deleteObject call does.

I have a feeling it is something very simple I'm missing or not doing correctly to cause this behavior. The data works great on my tableviews - its only when trying to update I get the crashes.

I have spent days & days on this trying numerous alternative methods. Whats left of my hair is falling out. I'd be willing to ante up some cash for anyone willing to look at my code and see what I'm doing wrong. Just need to get past this hurdle.

Thanks in advance for the help!

Answer 1

Did you save the context after removing the objects in the for loop? Be aware that deleteObject: does not delete the object immediately, it simply schedule it for deletion when changes are committed, i.e., when you save the context.

EDIT: Your problem may be related to how you present your data to the user on your table view. Without additional code is difficult to tell exactly (are you using NSFetchedResultsController or not?), but my guess is that the interaction between deleting the data and showing them on the table is not correct. Probably, what is happening is that your table is told to visualize your data, but then, when you delete them, you are not updating correctly the table.

Answer 2

Wow, so after a few days of testing I went down a path that led me to tracking down Zombies & memory mgmt. This was a situation where the errors I was recieving were leftover from issues in another area. When parsing the data and placing it into Core Data I released an object that was to be autoreleased. So any subsequent calls to that item within core data (save, deletec, etc) caused a crash. Thank you all for your help and I vow to pay closer attention with my memory mgmt calls.