Core Data: DELETE WHERE

Question

I know how to use NSPredicate to perform a SQL SELECT-like operation. How can I perform something like DELETE WHERE? Do I have to call [NSManagedObjectContext deleteObject] for each fetched object? Thanks

NSError *error;

NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:[NSEntityDescription entityForName:TASK_ENTITY inManagedObjectContext:managedObjectContext]];

NSPredicate *predicate = [NSPredicate predicateWithFormat: @"label LIKE  %@", label];
[request setPredicate:predicate];

NSArray *array = [managedObjectContext executeFetchRequest:request error:&error];

[managedObjectContext deleteObject:[array objectAtIndex:0]];

Answer 1

I believe looping over the returned array and calling [NSManagedObjectContext deleteObject:] is the "correct"/idiomatic way to do it. It might seem inefficient, but remember that the fetch command doesn't actually fetch the objects' data, and the deleteObject: method just marks the object for deletion, which gets applied when you send [NSManagedObjectContext save:]. Not knowing the internals of Core Data I can't tell you whether it's as efficient as a DELETE WHERE query (presumably Core Data has the indexed primary keys in memory from the fetch, and uses those) but in my experience with profiling Core Data apps it's not significantly slower than saving new or updated objects.