Question

I am trying to update an existing record in a database using CoreData, but I am getting an exception when using the Managed Object accessor method.

Code excerpt:

NSManagedObjectContext *tmpManagedObjectContext = [self.fetchedResultsController managedObjectContext];

NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Contact" inManagedObjectContext:tmpManagedObjectContext];
[request setEntity:entity];

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"contact_id = %@", [dict objectForKey:@"contact_id"]];
[request setPredicate:predicate];

NSError *error = nil;
[request setResultType:NSDictionaryResultType];
[request setPropertiesToFetch:[NSArray arrayWithObjects:@"first_name",@"sync_status",nil]];

Contact *contact = [[managedObjectContext executeFetchRequest:request error:&error] objectAtIndex:0];
contact.sync_status = @"Y";

error = nil;
if (![tmpManagedObjectContext save:&error]) {
    NSLog(@"Error setting sync status on contact record - error: %@", [error localizedDescription]);
}

The line that is causing the error is:

contact.sync_status = @"Y";

Error is * Terminating app due to uncaught exception ‘NSInvalidArgumentException’, reason: ‘-[NSKnownKeysDictionary1 setSync_status:]: unrecognized selector sent to instance 0x8907fd0’
* First throw call stack:

Contact is a NSManagedObject class which I automatically generated in Xcode.

Is my approach incorrect here? I haven’t had any problems with retrieving or deleting records, but I am stumbling on how to update data.

Any guidance or help would be greatly appreciated. Thanks.

Answer 1

You’ve configured your fetch request to return dictionaries instead of managed objects. If you want to update the returned objects, you must ask for them in the fetch request – that is, use the default behaviour instead of what you are doing.

Remove these lines:

[request setResultType:NSDictionaryResultType];
[request setPropertiesToFetch:[NSArray arrayWithObjects:@"first_name",@"sync_status",nil]];

And you’ll be fine. The lines above are used if you only want to return certain properties in the fetch, but you want the whole object.